Faradic porosity cell

ABSTRACT

Applicant&#39;s faradic porosity cell combines adsorption (physical and capacitive) and faradic immobilization of a target species by optimizing electrode porosity, applied E, and Pourbaix operating regions. The optimization parameters are (i) physical adsorption; (ii) capacitive adsorption; (iii) electrochemical pH modulation; (iv) electrochemical peroxide (H2O2) generation; (v) electrodeposition (e.g., electroplating, electrophoretic deposition); (vi) electrochemical oxidation or reduction; (vii) precipitation; (viii) pore mouth diameter profile, and (ix) electrode spacing, and (xi) flow-by vs. flow-through vs. carbon block cell design.

RELATED APPLICATIONS

This application claims the benefit of (i) U.S. application Ser. No.62/702,286 by Boehme et al., entitled “Capacitive Coagulation Cell”,filed on 23 Jul. 2018, (ii) U.S. application No. 62/758,433 by Boehme etal., entitled “Electro-Dechlorination Cell”, filed on 9 Nov. 2018, and(iii) U.S. application Ser. No. 16/417,574 by Lippert et al., entitled“Defined Carbon Porosity for Enhanced Capacitive Charging”, filed on 20May 2019.

FEDERAL FUNDING

The research leading to the invention disclosed herein was partiallyfunded by NIH-National Institute of Environmental Health Sciences PhaseI SBIR award number 1R43ES028171-01.

BACKGROUND OF THE INVENTION Field of the Invention

The field of the invention is removal of metal ions, halide ions,derivatives of metals and halides, and ionic particulates fromsolutions, e.g., the removal of lead from water, by pairing selectedfaradic reactions with carbon electrode pore mouth diameter profiling.

Definitions

“Adsorption” means attracting ions in an input stream to and retainingthose ions on an electrode surface.

“Agglutination” means removing metal ions, halide ions, derivatives ofmetals or halides, or particulate metal from an input stream to a cellby one or more of the following: (i) physical adsorption; (ii)capacitive adsorption; (iii) electrochemical pH modulation & metalimmobilization; (iv) electrochemical peroxide (H₂O₂) generation & metaloxidation; (v) electrodeposition or electroplating; (vi) electrochemicaloxidation or reduction; (vii) precipitation; (viii) pore mouth diameterprofile, (ix) electrode treatment, (x) electrode spacing, and (xi)flow-by vs. flow-through vs. carbon block cell design.

“BET surface area” means surface area determined by theBrunauer-Emmett-Teller method, which is a physical adsorption-basedmethod using nitrogen to determine the surface area of a material.

“Breakthrough curve” means the course of an effluent adsorptiveconcentration at the outlet of a fixed adsorber. A breakthrough curveenables the calculation of a technically usable sorption capacity.Breakthrough curves typically plot target species concentration vs.volume treated. See, e.g., FIG. 14 (FIGS. 14a-14c ).

“Carbon block” is an extruded carbon material with carbon particlesbound with a polymer into a bulk solid form. It is typically used fordechlorination and particle filters. In a carbon block cell design usedin an FPC, each of one or more pristine carbon blocks are typicallydivided into two halves that are electrically isolated in an FPC; onehalf or each block is used as an anode and the other half of each blockis used as a cathode.

“Capacitive adsorption” means adsorption of an ion or other chargedspecies on an electrode as a result of electrical attraction.

“CCC” or “capacitive coagulation cell” or “CCC device” means apurification cell that primarily uses capacitive adsorption to removemetal ions, derivatives of metals, or particulate metal from a liquid(typically aqueous) input stream and produce an output stream with ametal, metal derivative, or particulate content below a governmentregulated limit. For instance, the US EPA specifies a lead content of 15ppb as the “action level” for potable or irrigation water.

“CCC Parameter” means a user-selected FPC Parameter in an CCC.

“Cell” means, in general, a plurality of electrodes exposed to an inputstream (influent), with an outlet for the output stream (effluent)during operation, a short-circuit switch or power supply attached to theelectrodes, a manual or computerized means of controlling the powersupply and any in-stream valves, and sensors that monitor cell operationand interface with the manual or computerized means of control. A cellcan optionally include a further means of controlling the input streamand the output stream, for instance to select different output streamcollection vessels or other dispositions during cell operation. Unlike acapacitive deionization cell, an FPC does not regenerate (aka desorb)the electrodes to produce a waste stream of desorbed target speciesduring operation; instead, an FPC, including CCC or an EDC, is replaced,e.g., when the concentration of a target species in the output streamexceeds a user-selected threshold; replacement criteria other thantarget species concentration in the output stream, e.g., cumulativevolume of through stream for a given FPC, and presence of certainreaction byproducts, may be specified.

“Charging potential” means a voltage applied to a cell to perform work.

“Conductivity” means the electrical conductivity of an input stream,through stream, output stream, or a waste stream. Conductivity is asurrogate measurement for the molarity of ions in an input stream,output stream, or waste stream. Conductivity is directly proportional tomolarity of ions in such streams.

“CG” means a carbon that has a predominately mesoporous structure with anominal surface area of ˜700 m²/g. CG was formulated by the inventorsusing the pore mouth diameter profile method disclosed herein andfabricated for the inventors by Calgon Corporation (Naperville, Ill.).CG is sometimes recited as Calgon® in the Tables.

“CV” means cyclic voltammogram.

“CX” means carbon xerogel. CX electrodes possess a mesoporous structurewith a nominal surface area of ˜200 m²/g.

“Cycle” means a cycle of operation in which a sequence of positive thennegative, or negative then positive, potential has been applied to anFPC electrode.

“DO” means dissolved oxygen.

“E” means a voltage, aka electrical potential; if a direct current, Ehas a constant polarity (positive or negative).

“Electrode” means a material, typically porous carbon, which iselectrically conductive.

“EDC” means an electro-dehalidation cell disclosed in this Application.An EDC is a species of water purification cell within the genus of FPCs.

“EDC Parameter” means a user-selected FPC Parameter in an EDC.

“EDX” means Energy Dispersive X-Ray Analysis.

“E_(o)” is the potential vs. a reference electrode when the electrodesare short-circuited (i.e., E_(o) is the potential during a short-circuitcondition).

“E_(PZC)” or “potential of zero charge”, means the potential of anelectrode at which there is a minimum in ion adsorption at the surface.E_(PZC) can be intentionally shifted by surface modification of a carbonelectrode, or inherently relocated as a result of oxidation of anelectrode surface by extended applied potential or voltage. The E_(PZC)of a pristine carbon a electrode is typically between −0.1 V and +0.1 V.Shifting the E_(PZC) of an electrode through surface modifications isdisclosed in detail in U.S. application Ser. No. 62/702,286 incorporatedherein. FPC electrode E_(PZCS) for a given target species vary by waterchemistry and are empirically determined.

“Faradic immobilization” means electron transfer to a target species inthe electrolyte, or electron transfer to a species in the electrolyte,followed by a homogeneous reaction in solution with the target speciesof interest, after which the reaction product is adsorbed on anelectrode.

“Flow-by” cell design means the through stream in an FPC flows acrossthe surface of the electrodes in an FPC, rather than through theelectrodes. Flow-by cell design can provide the following advantagescompared to a flow-through cell design: lower pressure drop, higher flowrate, equal degradation of carbon electrodes, equivalent pH regionsgenerated for each electrode pair.

“Flow rate” means the flow rate, typically in L/hr, ml/min, etc., of aninput, throughput, output, or waste stream.

“Flow-through” cell design means the through stream in an FPC is forcedthrough the electrodes in an FPC. Flow-through cell design can providethe following advantages compared to a flow-by cell design: more extremepH regions, better control over outlet pH.

“FPC” or “faradic porosity cell” or “FPC device” means a purificationcell that uses agglutination to remove metal ions, halide ions,derivatives (e.g., other species) of target metals or target halides, orparticulate metal from a liquid (typically aqueous) input stream andproduce an output stream with a decreased metal, halide, or particulatecontent. Different species of FPC can be used in series or in parallelto remove target species from an aqueous influent to a purificationsystem. An “FPC system” means a water purification system that containsone or more FPCs and optionally other types of purification cells (seedefinition of “hybrid system”), such as capacitive deionization (“CDI”)cells, membrane CDI cells (“MCDI”), inverted CDI (“i-CDI”) cells, andnon-electrochemical cells and filters. Inclusion of CDI, MCDI, i-CDIcells, or similar desorbing cells in an FPC system requires provision ofa waste stream and associated cell controls in an FPC system toaccommodate desorption from CDI, MCDI, i-CDI, and similar desorbingcells into the waste stream. CCCs and EDCs are species of FPCs.

“FPC Parameter” means a user-selected value in an FPC of (i) physicaladsorption; (ii) capacitive adsorption; (iii) electrochemical pHmodulation; (iv) electrochemical peroxide (H₂O₂) generation & oxidationof target species; (v) electrodeposition (e.g., electroplating,electrophoretic deposition); (vi) electrochemical oxidation orreduction; (vii) precipitation; (viii) pore mouth diameter profile, (ix)electrode treatment, (x) electrode spacing, and (xi) flow-by vs.flow-through vs. carbon block cell design. One or more FPC Parametersare selected, or “tuned”, to remove a target species from a throughstream, based on empirical data for a given input water chemistry.

“Halide derivative” means a molecule or compound that contains a halide.

“HE” means a high-efficiency mesoporous carbon. Electrodes made with HEcarbon possess a predominately mesoporous structure with a nominalsurface area of −380 m²/g. HE has a formulation of >98% mesoporouscarbon with the balance being macroporous carbon. HE is formulated usingthe pore mouth diameter profile method disclosed in U.S. applicationSer. No. 62/702,286 incorporated herein.

“Hybrid system” means a water purification system that contains at leastone FPC (CCC or EDC) and at least one other type of water purificationcell, e.g., a peroxidation cell, CDI, MCDI, i-CDI, ornon-electrochemical cell or filter. The minimal configuration of ahybrid system is series (FPC feeding other cell type, or vice versa).Larger systems can be series only, or have series paths in parallel (toincrease throughput).

“Immobilization” means adsorption of a target species on an FPCelectrode without later desorption into a purified output stream.

“Input stream” means a liquid, typically water containing various ionsand metals, admitted through an inlet to a cell.

“KN” means a microporous carbon marketed as Kynol® available fromAmerican Kynol, Inc (Pleasantville, N.Y.). Electrodes made with KNcarbon possess a microporous structure with a nominal surface area of˜1800 m²/g.

“Metal” means a metal, metal ion, metal complex, metal particle, ortoxin for which a Pourbaix diagram exists and containing a metalselected from the group comprising As, Se, Pb, Ni, Zn, Al, Sc, Ti, V,Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf,Ta, W, Re, Os, Ir, Pt, Au, Hg, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, and Lu.

“Metal derivative” means a molecule or compound that contains a metal ormetalloid.

“Metal speciation” means the different chemical forms (“species”) of ametal in a given milieu. For instance, As(III) and As(V) are species ofarsenic that can coexist in an aqueous solution at a given pH.

“NHE” means Normal Hydrogen Electrode.

“Output stream” means a liquid that has passed through an FPC andcontains a lower molarity of target species than in the input stream.

“Parallel system architecture” means FPCs (and optionally other types ofcells and filters) connected in parallel, i.e., the outlet of each FPC(and optionally other types of cells and filters) feeds the systemoutput. A parallel system architecture can be fixed, or can comprisemultiple FPCs, a process controller, interconnecting lines, sensors, andvalves disposed in the lines and cells.

“Physical adsorption” means physical entrapment of a target species inan electrode pore.

“PMD” means pore mouth diameter, which is the diameter of a pore on thesurface of a carbon electrode. A pore may be a dead-end channel or athrough channel within a carbon electrode, and typically has a variablechannel diameter.

“Point of entry” or “POE” means the location where a water supply feedsa water distribution system in a residence, commercial/industrialbuilding, or other structure.

“Point of use” or “POU” means the location where water is dispensed froma water distribution system to a consumer, beverage dispenser, kitchenappliance, or other end use.

“Polarity” means the polarity of a DC voltage, either positive ornegative.

“Pore mouth diameter profile” means the volumetric ratio(s) amongmicroporous, mesoporous, and macroporous carbon in an electrodefabricated according to the pore mouth diameter profile method disclosedin U.S. application Ser. No. 62/702,286 and U.S. application Ser. No.16/417,574 incorporated herein. Generally speaking, the larger theaverage pore mouth diameter, the longer the working lifetime of theelectrode and the more permeable the electrode is to a through stream.The average pore mouth diameter is controlled by the ratio ofmicroporous, mesoporous, and macroporous carbon used to fabricate agiven carbon electrode.

“Pourbaix diagram” (aka potential/pH diagram, EH-pH diagram or a pE/pHdiagram), maps out possible stable (equilibrium) phases of an aqueouselectrochemical system. Predominant ion boundaries are represented bylines. As such, a Pourbaix diagram can be read much like a standardphase diagram with a different set of axes. Similar to phase diagrams,Pourbaix diagrams do not address reaction rate or kinetic effects. Forsoluble species, the lines in a Pourbaix diagram are usually drawn forconcentrations of 1 M or 10⁻⁶ M. Sometimes additional lines are drawnfor other concentrations.

“Pourbaix operating region” means relating the pH and applied E at agiven electrode in an FPC to a Pourbaix diagram to select forimmobilization of a target species in a given water chemistry.

“Pristine” in reference to electrodes means without surfacemodifications; for example, a Spectracarb™ electrode, as supplied by themanufacturer, is pristine.

“Process controller” means a computer operating a process controlapplication that monitors sensors disposed in a system of FPCs (andoptionally, other types of cells and filters) to sample input, through,and/or output streams and status of FPCs (and optionally, other types ofcells and filters) in a water purification system comprising one or moreFPCs and optionally one or more other types of water purification cellsor filters. The process controller actuates valves in linesinterconnecting a source of aqueous solution to be treated, FPCs (andoptionally other cells and filters), and system outlets, therebyenabling the various FPCs (and optionally other cells and filters) to beconfigured in a series system architecture, series-parallel systemarchitecture, or parallel system architecture. Based on sensor data, theprocess controller can dynamically adjust FPC Parameters of FPCs in thesystem (and optionally adjust other cells and filters in the system).

“Purify” means to remove one or more target species from a throughstream. Purification includes the removal of metals for which a Pourbaixdiagram exists (e.g., As, Pb, Ni, Zn, Al, Cr, Mn, Fe, and Cu), halides(e.g., Cl, Br, chloramines), organics, and biological compounds.

“Rolled cell design” means an FCP cell design in which continuousseparator and porous carbon-based electrode materials are physicallyrolled into a spiral to create a cylinder with multiple, predominantlyflow-by, through stream paths through the porous carbon electrodes. Tomake a rolled cell, sheets of anode material, separator material, andcathode material are stacked and then rolled up to form a cylinder.Current collectors are attached to the anode and the cathode, usually inmultiple locations to reduce electrical losses.

“SC” means a microporous carbon marketed as Spectracarb™ available fromEngineered Fibers Technology, LLC (Shelton, Conn.). Electrodes made withSC carbon possess a microporous structure with a nominal surface area of˜1900 m²/g.

“SCE” means a saturated calomel electrode, a standard referenceelectrode commonly used as a reference electrode, e.g., in cyclicvoltammetry.

“Series system architecture” means FPCs (and optionally, other types ofcells and filters) connected in series, i.e., the outlet of a first FPCfeeds the inlet and a second FPC, the outlet of the second FPC feeds theinlet and a third FPC, and so on. A series system architecture can befixed, or can comprise multiple FPCs (and optionally, other types ofcells and filters), a process controller, sensors, interconnecting feedlines, and valves disposed in feed lines between the outlet of one FPCand the inlet of a second FPC.

“Series-parallel system architecture” means a system in which FPCs (andoptionally, other types of cells and filters) can be connected in seriesor in parallel. A series-parallel system architecture can be fixed, orcan comprise multiple FPCs (and optionally, other types of cells andfilters), a process controller, interconnecting feed lines, sensors, andvalves disposed in feed lines between the outlet of one FPC and theinlet of a second FPC, which valves are actuated by the processcontroller. The typical series-parallel system architecture comprisesmultiple ranks of a given series of cells, thereby treating the throughstream in the same way, but with higher throughput provided by multipleserial paths.

“SHE” means Standard Hydrogen Electrode.

“Shift” means to alter the potential (aka “location”) of the E_(PZC) ofan electrode by intentional or unintentional chemical or electrochemicalmodification of the electrode surface (e.g., electrochemical oxidationdue to an applied potential or voltage) using the methods disclosed inU.S. application Ser. No. 62/702,286 incorporated herein.

“Species” means a molecule, compound, or particulate in an aqueousstream or adsorbed on a cell electrode.

“Speciation” means the distribution of an element among defined chemicalspecies in a system or within an FPC. For instance, an uncharged metalparticle, a metal ion, and a metal complex of a given metal may coexistin solution or suspension at a given pH, which distribution may changeas pH changes.

“Stacked cell design” means an FCP cell design in which separate piecesof separator and porous carbon-based electrode materials are stackedlayer-by-layer to create a cylinder with multiple, predominantlyflow-by, through stream paths through and/or by the porous carbonelectrode. Current collectors are attached to the anode and the cathode,usually in multiple locations to reduce electrical losses. FIG. 23 showsa stacked cell design.

“Surface-charge enhanced surface” means an electrode surface that hasbeen imparted with surface charge through chemical or electrochemicalmethods.

“System” is a plurality of interconnected FPCs (and optionally, othertypes of cells and filters) controlled manually or by a processcontroller.

“Target metal” means one or more species of a given metal or metalderivative to be removed using a CCC.

“Target speciation” means one of several ionic states or complexations atarget species may assume in an aqueous electrochemical cell as afunction of E applied to cell electrodes and pH, as shown in a Pourbaixdiagram of the target species.

“Target species” means a molecule, compound, or particulate to beremoved using an FPC. “Target species” includes not only the molecule,compound, or particulate as found (aka “identified as a species in aPourbaix diagram”) in the input stream to an FPC, but one or moreintermediate and final reactive products created in an FPC that includethat molecule, compound, or particulate.

“Through stream” means the liquid stream being treated within a cell;stated differently, the through stream means the stream within a celland between the inlet to the cell and the outlet from the cell.

“Treat” means to feed an input stream into an operating FPC or systemcontaining FPCs and to recover the purified output stream.

“Treated electrode” means an electrode with an electrode surfacemodification disclosed herein.

“TDS” means total dissolved solids. The general operational definitionis that the solids must be small enough to survive filtration through afilter with two-micrometer pores.

“Untreated electrode” means an electrode without an electrode surfacemodification disclosed herein, i.e., a pristine carbon electrode.

“Voltage” and “potential” are synonymous herein. Voltage is directcurrent (“DC”) unless otherwise specified.

“Waste stream” means a liquid that has passed through a CDI, MCDI, i-CDIcell, reverse osmosis, ion exchange, or other water purification cellthat cycles between adsorption and desorption and contains a highermolarity of ions than in the input stream. Deionization cells, e.g.,capacitive deionization cells, can be used in a system containing FPCs.An FPC does not have a waste stream: the output stream from an FPC ispurified water. A system that contains deionization cells thatperiodically desorb molecules will have (i) a purified output streamfrom deionization cells operating in an adsorption state that iscombined with FPC output streams, and (ii) a waste stream fromdeionization cells operating in a desorption state.

Related Art

Toxic metals, esp. lead, in drinking water and crop irrigation water area major, worldwide health problem. The problem, and health impacts, arelargely unreported until a crisis occurs, as when the water in amunicipal water system becomes toxic from lead contamination. At least18 million Americans were at risk of drinking lead-contaminated waterlast year. More than 5,000 community water systems violated a federallead rule. Elevated blood lead levels in children cause irreversibleneurological and behavioral disorders, and even low levels have beenlinked to decreased IQ and lifetime achievement. The U.S. EnvironmentalProtection Agency (“EPA”) emphasizes that there is no safe level of leadexposure. The most commonly used filters for residentialpoint-of-use/point-of-entry (POU/POE) lead reduction, e.g., filtersusing zeolites and ion exchange, fall short—they have limited effectivelifetimes, lack substantial lead specificity, and are expensive.

FIG. 1 shows U.S. locations with dangerously high levels of lead inmunicipal drinking water and the incidence of elevated blood lead levelsin young children in the U.S., exposing them to a risk of permanentbrain damage, seizures, coma, and even death from lead poisoning. TheU.S. Natural Resources Defense Council (“NRDC”) recently found 5,363community water systems in violation of the EPA's lead and copper rule(https://www.epa.gov/dwreginfo/lead-and-copper-rule), a federalrequirement for monitoring of lead and copper levels in water. The NRDCreport also found 1,110 water systems that exceed the action level forlead (15 ppb in at least 10 percent of homes tested). These systemscollectively serve nearly 4 million people. The EPA is consideringrevising the 1991 Lead and Copper Rule to make regulations morestringent, and an Administrator of the EPA stated that the agency isworking on an ambitious 10-year strategy to “declare a war on lead” anddescribed lead in drinking water as “one of the greatest environmentalthreats we face as a country”.

One 2018 test of the municipal water system in Flint, Mich., showed leadlevels of 13,000 ppb, which is 866-times the EPA action level for leadin drinking water. The population is becoming more aware andincreasingly concerned about the water quality at home, in schools, andin the community. Water fountains in public schools in New York,California, Ohio, and Illinois have tested well above the action levelof 15 ppb. Despite corrosion prevention measures taken by public waterauthorities to minimize the risk of pipes leaching lead into thedrinking water system from outdated infrastructure, lead concentrationsin drinking water are commonly elevated nationwide. The most effectiveway to eliminate lead from drinking water is to replace lead lines, aneffort that would cost an estimated $30 billion. A better POU/POE devicefor potable water would be a vastly easier and more cost-effectivesolution. The problem of lead contamination is underserved because theexisting solutions are overwhelmed by high expense, poor efficacy,and/or short device lifetimes.

Lead removal devices currently on the market lack specificity for lead,and device lifetime is limited by the total amount of water volumefiltered, regardless of lead concentration. Over time the pressure dropacross the filter becomes so large that water can no longer flow throughthe filter, even if the adsorbent in the filter is not fully consumed,rendering it useless.

Chlorine and/or chloramines are routinely added to the US drinking watersupply as disinfectants to control microbial growth. While the removalof microbes is beneficial for human consumption, chlorine and/orchloramine contributes to tap water's unpleasant taste and odor.Therefore, removing chlorine and chloramines before end use isdesirable. Chlorine is more volatile than chloramine and easier toremove with a typical consumer's filter pitcher; however, to removechloramine, specially formulated filters containing activated carbon(catalytic carbon) are required. The presence of chlorine and/orchloramines is also detrimental for water purification processes thatrely on polymer membranes, such as reverse osmosis (RO). Most membranesare not resistant to these disinfectants and break down upon exposure,causing irreversible damage and replacement of expensive RO membranes.Drinking water and other water for use in heat and power plants andother industrial processes (“process water”) must have chlorine,chloramines, and other halides (esp., bromine and iodine) and halidederivatives removed to reduce corrosion and fouling of process systems.A solution for the technical problem of removing both chlorine andchloramines from water sources without damaging RO membranes and withreduced use of activated carbon filters would not only reduce waterpurification costs, but improve drinking water and process waterquality. Oxidation of water-borne contaminants, as a water purificationprocess, is normally done with hydrogen peroxide or ozone. Oxidation ofcertain water-borne contaminants facilitates further degradation andultimate destruction of the contaminants without further intervention.

The technical problem to be solved is to provide (i) a more efficient,less expensive, purification device to produce purified water,especially a device that removes soluble and insoluble lead to below 15ppb in potable water, which purification device is (ii) easily scalablefor residential, municipal, commercial, and industrial use. Applicanthas developed a faradic porosity cell (“FPC”) that solves the technicalproblem by agglutination of target species. Two genera of the FPC aredisclosed herein: a first genus that uses a novel electro-dehalidationtechnology to remove chlorine, other halides, chloramine disinfectants,and other halide derivatives from water—called herein theelectro-dehalidation cell (“EDC”); and a second genus that uses a novelcapacitive coagulation technology to remove metals, metal derivatives,and particulate metal—called herein the capacitive coagulation cell(“CCC”). Applicant's faradic porosity technology is significantly moreeffective in water purification than commonly used processes such aschemical coagulation, ion-exchange, and adsorbents. The EDC solves thetechnical problem of reducing the cost, and improving the efficiency, ofremoving chlorine, chloramines, and other halides and halide derivativesfrom drinking water and from process water. The CCC solves the technicalproblem of reducing the cost, and improving the efficiency, of removingmetal, metal derivatives, and particulate metal from drinking water andfrom process water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. A map the National Resources Defense Council produced ofcounties with water systems in violation of the EPA's Lead and CopperRule (left), and number of cases of children with elevated blood leadlevels in 2012 (right).

FIG. 2. Schematic of part of a CCC core. The schematic shows 2 pairs(anode and cathode per pair) of electrodes in a CCC core. A CCCtypically has more than 10 pairs of electrodes.

FIG. 3. Lead removal comparison of Applicant's CCC device tocommercially available prior art POU devices. Applicant's CCC, denotedas “PTW” in FIG. 2, was tested with different municipal waterchemistries that had lead content above the EPA action level.Applicant's CCC outperformed all prior art devices.

FIG. 4. Pourbaix diagram of lead (Pb) in a carbonate solution showingthe Pourbaix operating regions for lead species removal at theintersection of E applied to anode and cathode and resultant pH neareach electrode.

FIG. 5. Agglutination mechanisms for lead (Pb) removal showing leadspeciation and pathways for immobilization of Pb species.

FIG. 6. Pourbaix diagram for hypochlorite. (Debiemme-Chouvy, Catherine &Hua, Y & Hui, F & Duval, Jean-Luc & Cachet, H. (2014). Corrigendum to“Electrochemical treatments using tin oxide anode to prevent biofouling”[Electrochimica Acta 56/28 (2011) 10364-10370]. Electrochimica Acta.121. 461. 10.1016/j.electacta.2014.01.130.)

FIG. 7. Pourbaix diagram for hypobromite. (Ibid.)

FIG. 8. Pourbaix diagram for mono chloramine (NH₂Cl).(www.sedimentaryores.net/Pipe %20Scales/Chlorine-chloramine.html)

FIG. 9. Charge passed with commercially available microporous carbon[Spectracarb (SC) and Kynol (KN)], a predominately mesoporous carbon[Calgon (CG)], a mesoporous carbon [Carbon Xerogel (CX)], and theinventor's high-efficiency (HE) carbon electrodes, while cycling betweenapplied and short-circuited voltages. The order of the carbon types inthe legend is also the order of the starting specific charge passed(y-axis) traces, except CX has a lower y-axis value than HE.

FIG. 10. Potential distribution for Kynol electrodes in a 4-electrodeset-up in 4.3 mM NaCl, where pristine Kynol was the anode and cathode,Pt was the counter-electrode, and a standard calomel electrode (SCE) wasthe reference. The voltage was applied in 0.2 V increments from 1.6 Vdown to 0.8 V and back up to 1.6 V. E_(0,avg) represents the opencircuit voltage of the system.

FIGs. 11a-e . FIGS. 11a-e show cyclic voltammograms (CV) at a scan rateof 0.5 mV/s in 4.3 mM NaCl with carbon as the working electrode, Ptcoated Ti as the counter-electrode, and a standard calomel electrode(SCE) as the reference. The CVs were collected using a carbon electrode(different types, as identified), disposed in an electrolyte and held atconstant voltage and for a uniform experimental duration. The voltageapplied between anodes and cathodes is ramped up then ramped down at thescan rate, and the current response recorded as a CV. In addition to aCV of pristine (0 h) electrodes, each plot shows the results (3 h and 6h traces) of accelerated oxidation studies performed after use of theelectrodes at a constant applied potential of 2.0 V for 3 and 6 hours.

FIG. 11a shows CVs for microporous SC. After 3 hours of electrochemicaloxidation, the E_(PZC) has shifted to the right, indicative of theformation of covalent bonds between the oxygen-containing functionalgroups and the carbon surface of the carbon electrode. After 6 hours,the electrical potential of zero charge (E_(pzc)) is no longer presentand there is a noticeable decrease in current, signifying pore collapse.The same trend is observed in FIG. 11b for microporous KN.

FIG. 11b shows CVs for microporous KN, which shows the same trend asmicroporous SC in FIG. 11 a.

FIG. 11c shows CVs for CG, a primarily mesoporous carbon. After 3 and 6hours of electrochemical oxidation, the E_(PZC) has shifted to theright, but the current is maintained due to non-collapsed pores.

FIG. 11d shows CVs for mesoporous CX, which follows the same trendobserved for CG in FIG. 11 c.

FIG. 11e shows CVs for mesoporous HE, which also follows the same trendobserved for CG in FIG. 11c , but HE exhibits more area within the CVplot at 3 h and 6 h compared with CX in FIG. 11d due to a higherelectrochemically active surface area, which provides a larger currentresponse; the pore size of CX in FIG. 11d is 10× larger than HE, whichis related to stability of the electrode and ultimate lifetime; thelarger pore size of CX, however, provides much less surface area thanHE.

FIG. 12. Bench-scale capacitive coagulation device.

FIG. 13. SEM micrographs and EDX mapping showing the end fate ofimmobilized lead species. Carbon (C), lead (Pb), and oxygen (O) aremapped in the three panels below, represented by the lightest contrastin each corresponding gray scale image. The carbon electrodes are shownas black and the copper as gray in the grayscale equivalent of thephoto. Color photograph of EDX mapping is available.

FIGS. 14a-14c . Breakthrough curves for prior art activated carbonpacked column (panel in FIG. 14a ) and Applicant's CCC device (panels inFIG. 14b and FIG. 14c ) experiments. The y-axis on the left has beennormalized for the initial lead concentration: (a) 126 ppb, (b) 296 ppb,and (c) 10,000 ppb. The y-axis on the right shows the total Pb removedin mg for the volume treated.

FIG. 15. DO reduction at 1.2 V. DO reduction generates hydrogenperoxide, a potent oxidizer.

FIG. 16. Pourbaix diagram for Pb. (Schock, M. R., Hyland, R. N., andWelch, M. M. (2008). Occurrence of contaminant accumulation in lead pipescales from domestic drinking-water distribution systems. Environ. Sci.Technol. 42(12), 4285-4291)

FIG. 17a shows a Pourbaix diagram for Cu showing methods of removal ofcopper hydroxide [Cu(OH)2] formation.

FIG. 17b shows a Pourbaix diagram for Cu showing methods of copperelectrodeposition or electroplating [Cu(s)].(https://commons.wikimedia.org/wiki/File:Cu-pourbaix-diagram.svg).

FIG. 18. Pourbaix diagram for Ni. (Ciesielczyk, F., Bartczak, P.,Wieszczycka, K., Siwinska-Stefanska, K., Nowacka, M., and Jesionowski,T. (2013). Adsorption of Ni(II) from model solutions usingco-precipitated inorganic oxides. Adsorption. 19, 423-434.)

FIG. 19. Pourbaix diagram for Fe.(https://commons.wikimedia.org/wiki/File:Pourbaix_Diagram_of_Iron.svg)

FIG. 20. Pourbaix diagram for Mn.(https://commons.wikimedia.org/wiki/File:Mn_pourbaix_diagram.png)

FIG. 21. Pourbaix diagram for Al.(https://corrosion-doctors.org/Corrosion-Thermodynamics/Potential-pH-diagram-aluminum.htm)

FIG. 22. Pourbaix diagram for Zn.(https://commons.wikimedia.org/wiki/File:Zn-pourbaix-diagram.svg)

FIG. 23. Schematic of an EDC device with stacked cell design. The feed(influent, or input stream) flows in the bottom of the device, proceedsthrough an annular space near the wall of the cell housing, then flowscentripetally over the electrode surfaces to the axial channel, and isthen discharged (effluent or output stream) through the axial channel tothe FPC outlet. Feed spacers are optional; a feed spacer (shown in FIGS.23 and 29) is an additional layer of material between anode and cathodethat can optionally be added to create a larger flow channel for thethrough stream.

FIG. 24. Applied voltage and current transients as a function of volumetreated at a flow rate of 300-500 ml/min for EDC experiments conductedwith Calgon as both electrodes. Current spikes at ˜1500 and ˜1600gallons are due to noise (inadvertent physical movement of theelectrical leads) and can be neglected. At ˜1800 gallons, operation wasswitched from applying a constant voltage to applying a constant currentof ˜0.2 A, observed as a straight line. The voltage decay (voltage isreading as negative, but the total cell voltage is increasing withconstant current) seen at this condition is a consequence of applying aconstant current. The subsequent switching also occurred at constantcurrent, but the voltage reached the cutoff value quickly and the systemessentially behaved as though at constant voltage.

FIG. 25a shows copper deposition on the cathode at an applied potentialof 1.2 V.

FIG. 25b shows no copper deposition on the cathode at an appliedpotential of 1.2 V. The carbon electrodes are shown as black and thecopper as gray in the grayscale equivalent of the photo. Colorphotograph of copper deposited on the cathode available.

FIG. 26. Rust colored Fe-oxide deposits on the separators at the cathodesurface after experiment. The carbon electrodes are shown as black andthe iron as gray deposits on the white separators in the grayscaleequivalent of the photo. Color photograph of copper deposited on thecathode available.

FIGS. 27a shows carbon cloth with white precipitates.

FIG. 27b shows scanning electron microscopy (SEM) micrographs of thecloth showing a Pb crystal.

FIG. 28. EDX mapping of a Pb crystal from FIG. 27 confirming that thecrystal is lead oxide by the presence of both lead and oxygen. Carbon(C), lead (Pb), and oxygen (O) are mapped in the three panels to theright, represented by the lightest contrast in each corresponding grayscale image. Color photograph of EDX mapping is available.

FIG. 29. Schematic of a rolled cell design in which continuous separatorand porous carbon-based electrode materials are physically rolled into aspiral to create a cylinder with multiple, predominantly flow-by,through stream paths through the porous carbon electrode.

FIG. 30. EDC experiments conducted with Kynol as both electrodes.Concentration of total chlorine in the feed and product streams, andapplied voltage, as a function of volume treated at a flow rate of 500ml/min is shown.

FIG. 31. EDC experiments conducted with Kynol as both electrodes.Concentration of free chlorine in the feed and product streams, andapplied voltage, as a function of volume treated at a flow rate of 500ml/min is shown.

FIG. 32. EDC experiments conducted with Kynol as both electrodes.Concentration of chloramine in the feed and product streams, and appliedvoltage, as a function of volume treated at a flow rate of 500 ml/min isshown.

FIG. 33. EDC experiments conducted with Kynol as both electrodes.Percent removal of total chlorine, free chlorine, chloramine, andperoxide after treatment of tap water with the EDC, and applied voltage,as a function of volume treated at a flow rate of 500 ml/min is shown.

FIG. 34. EDC experiments conducted with oxidized Kynol as one electrodeand Fuel Cell Earth as the other. Concentration of total chlorine in thefeed and product stream, and applied voltage, as a function of volumetreated at a flow rate of 300-500 ml/min.

FIG. 35. EDC experiments conducted with oxidized Kynol as one electrodeand Fuel Cell Earth as the other. Concentration of free chlorine in thefeed and product stream, and applied voltage, as a function of volumetreated at a flow rate of 300-500 ml/min.

FIG. 36. EDC experiments conducted with oxidized Kynol as one electrodeand Fuel Cell Earth as the other. Concentration of chloramine in thefeed and product stream, and applied voltage, as a function of volumetreated at a flow rate of 300-500 ml/min.

FIG. 37. EDC experiments conducted with oxidized Kynol as one electrodeand Fuel Cell Earth as the other. Percent removal of total chlorine,free chlorine, chloramine, and peroxide after treatment of tap waterwith the EDC, and applied voltage, as a function of volume treated.

FIG. 38. EDC experiments conducted with Calgon as both electrodes.Concentration of total chlorine in the feed and product stream, andapplied voltage, as a function of volume treated at a flow rate of300-500 ml/min.

FIG. 39. EDC experiments conducted with Calgon as both electrodes.Concentration of free chlorine in the feed and product stream, andapplied voltage, as a function of volume treated at a flow rate of300-500 ml/min.

FIG. 40. EDC experiments conducted with Calgon as both electrodes.Concentration of chloramine in the feed and product stream, and appliedvoltage, as a function of volume treated at a flow rate of 300-500ml/min.

FIG. 41. EDC experiments conducted with Calgon as both electrodes.Percent removal of total chlorine, free chlorine, chloramine, andperoxide after treatment of tap water with the EDC, and applied voltage,as a function of volume treated.

SUMMARY OF THE INVENTION

To increase the efficiency of removal of metal and halide contaminantsfrom water using an electrochemical device that typically operates undera constant applied potential, Applicant's combining of capacitiveadsorption, faradic reactions near or on cell electrodes, and electrodepore mouth diameter profiling creates a new type of electrochemicaldevice, the faradic porosity cell. The first consideration in a faradicporosity cell is the selection and use of carbon-based materials thatcan generate reactions and vary pH at both the anode (carbon oxidationwith water) and the cathode (dissolved oxygen reduction) over longperiods of time. Carbon materials with the right porosity and bulkmaterials properties can produce these reactions over extended timeperiods, which will enable targeted reactions with incoming constituents(target species) to be removed from an aqueous solution.

The next design consideration is spacing between the anode and thecathode. With decreased spacing, while maintaining electrical isolationbetween the electrodes, faster reaction rates are possible, which willlimit the residence time needed for certain “reaction andimmobilization” processes to be accomplished. Electrode spacing istypically less than 1 mm, and is preferably as close as possible withoutcausing a short circuit of anode and cathode or causing an unacceptablepressure drop (the corollary of which is increased residence time anddecreased flow rate) within the FPC. Preferable electrode spacing isless 1 mm, preferably less than 200 microns, more preferably less than50 microns, and most preferably less than 20 microns.

Some species of a target species will adsorb by physical entrapment(“physical adsorption”) on, or by electrical attraction (“capacitiveadsorption”) to, an electrode. Other species of a target species arestarting materials for reactions (typically, oxidation) that create,directly or indirectly, new species of the target species that areimmobilized on an electrode. Immobilization removes the target speciesfrom the solution. At a given spacing between the electrodes and matchedcarbon electrode materials properties, the potential applied to theanode and cathode are selected, based on the Pourbaix diagram of thetarget species in the input stream. Examples of FPC Parameters forvarious target species are shown in Table 1. For example, to removecopper, immobilization by plating on an electrode can occur atpotentials ranging from ˜0.3 V to −0.4 V vs. NHE for pH regions from 0to 14. In addition, precipitation can occur in the form of copperhydroxide (Cu(OH)₂) at the anode at potentials above 0 V vs. NHE and pHvalues higher than 4 (see FIG. 17). Total cell potentials ofapproximately 0.4 V are desired for the removal of copper in a faradicporosity cell.

TABLE 1 FPC parameters for various target species Anode CathodePreferred Preferred PMD Preferred Target Voltage Voltage Anode E_(PZC)Cathode E_(PZC) Range Operating Species Range (V) Range (V) Range (V)Range (V) (nm) Voltage (V) Pourbaix Reference Mn 0-1.2 <−1.1 −0.1-1.0−1.0-0.1 0-50 1.2 https://commons.wikimedia.org/wiki/File:Mn_pourbaix_diagram.png Fe 0-1.2 <−0.5 −0.1-1.0 −1.0-0.1 0-50 0.4-1.2https://commons.wikimedia.org/wiki/File: Pourbaix_Diagram_of_Iron.svgCo >0 <−0.5 −0.1-1.0 −1.0-0.1 0-50 \ Garcia, E. M, Santos, J. S.,Pereira, E. C., and Freitas, M. B. J. G. (2008). Electrodeposition ofcobalt from spent Li-ion battery cathodes by the electrochemistry quartzcrystal microbalance technique. J. Power Sources. 185(1), 549-553. Ni0-1.0 <−0.4 −0.1-1.0 −1.0-0.1 0-50 1.2 Ciesielczyk, F., Bartczak, P.,Wieszczycka, K., Siwinska-Stefanska, K., Nowacka, M., and Jesionowski,T. (2013). Adsorption of Ni(II) from model solutions using co-precipitated inorganic oxides. Adsorption. 19, 423-434.) Cu >0 <0−0.1-1.0 −1.0-0.1 0-50 0.8-1.2 https://commons.wikimedia.org/wiki/File:Cu-pourbaix-diagram.svg Zn >0 <−0.8 −0.1-1.0 −1.0-0.1 0-50 0.8-1.2https://commons.wikimedia.org/wiki/File: Zn-pourbaix-diagram.svg Al >0<−1.3 −0.1-1.0 −1.0-0.1 0-50 0.4https://corrosion-doctors.org/Corrosion-Thermodynamics/Potential-pH-diagram-aluminum.htm Pb >0.5 <−0.4 −0.1-1.0 −1.0-0.1 0-501.2 Schock, M. R., Hyland, R. N., and Welch, M. M. (2008). Occurrence ofcontaminant accumulation in lead pipe scales from domesticdrinking-water distribution systems. Environ. Sci. Technol. 42(12),4285-4291. Pourbaix M. J. N., Van Muylder, J., and de Zoubev N. (1959)Pd >0 <0 −0.1-1.0 −1.0-0.1 0-50 \ Electrochemical properties of theplatinum metals. Platinum Metals. Rev. 3(3), 100-106. Ag >0 <0 −0.1-1.0−1.0-0.1 0-50 \ Kortenaar, M. V., de Goeij, J. J. M, Kolar, Z. I.,Frens, G., Lusse, P. J., Zuiddam. M. R., and van der Drift, E. (2001).Electroless silver deposition in 100 nm silicon structures. J.Electrochem. Soc. 148(1), C28-C33. Ir >0.4 <0 −0.1-1.0 −1.0-0.1 0-50 \https://www.gamry.com/resources/electrochemical-calculators-tools/convert-potentials-to-another-reference-electrode/ Pt >0 <0−0.1-1.0 −1.0-0.1 0-50 \ Pourbaix M. J. N., Van Muylder, J., and deZoubev N. (1959) Electrochemical properties of the platinum metals.Platinum Metals. A new approach to studies of corrosion resistance andcathodic protection. Rev. 3(2), 47-53. Au >0.8 <0 −0.1-1.0 −1.0-0.1 0-50\ https://www.doitpoms.ac.uk/tlplib/pourbaix/ pourbaix_example.phpHg >0.3 <0 −0.1-1.0 −1.0-0.1 0-50 \https://commons.wikimedia.org/wiki/File:Pourbaix-hg.png Free Cl <1.5<−1.0 −0.1-1.0 −1.0-0.1 0-50 1-3 Debiemme-Chouvy, Catherine & Hua, Y &Hui, F & Duval, Jean-Luc & Cachet, H. (2014). Corrigendum to“Electrochemical treatments using tin oxide anode to prevent biofouling”[Electrochimica Acta 56/28 (2011) 10364-10370]. Electrochimica Acta.121. 461.10.1016/j.electacta.2014.01.130 Free Br <1.2 <−1.0 −0.1-1.0−1.0-0.1 0-50 \ Ibid Choramine <1.4 <−1.0 −0.1-1.0 −1.0-0.1 0-50 1-3www.sedimentaryores.net/Pipe%20Scales/ Chlorine-chloramine.html

Other target species can be removed under similar mechanisms but underdifferent voltage regions. For example, lead precipitation can occurfrom the pH and potentials that are generated on the electrode surfaces.At potentials more negative than ˜0.4 V vs. NHE and pH regions from 0 to14, lead can be plated as a solid at the cathode. Precipitation at theanode can also occur as PbO₂ if the pH is kept >1.5 and potentials >0.5V vs. NHE are used (FIG. 16). Finally, oxidation from H₂O₂ generated atthe cathode can also result in precipitation of target species. The rateof reduction of dissolved oxygen (“DO”) near the cathode depends uponthe oxidation of the cathode carbon, e.g., by oxidative shifting of thecathode E_(PZC), or as a result of use in situ.

Using the Pourbaix diagram for a material can define the pH and voltageneeded in a faradaic porosity cell to remove target species of interest.A faradic porosity cell comprises a series of porous carbon anodes andcathodes, typically consisting of reduced cathodes (negative E_(PZC) andpositive surface charge) and pristine anodes (although anodes experiencea positive E_(PZC) shift ((negative surface charge)) during use), andoperated by applying a small voltage, e.g., 1.2 V, across theelectrodes. A schematic of an CCC embodiment of an FPC is shown in FIG.2. An aqueous input stream to be purified is introduced into an FPCthrough an inlet to the cell; the electrodes in an FPC are immersed inthe aqueous stream and a target species is removed from the throughstream. After removal of a target species in an FPC, the through streamis discharged from the cell through an outlet for use, storage, orfurther processing. The electrodes of the cell are connected to a powersupply that can apply E+ or E− to a given electrode. A core inventivestep of an FPC is the precise matching of E+ applied to the cell anodesand E− to cell cathodes, pore mouth diameter profile of the electrodematerial, and selected Pourbaix operating region, thereby improvingpurification efficiency and improving cost/benefit. A Pourbaix diagramoperating region shows speciation based on applied E and pH. In an FPC,speciation is driven by the potentials, E+ and E−, applied to theelectrodes. Maintaining FPC operation in the selected Pourbaix operatingregion, with optimized pore mouth distribution (“PMD”) profileelectrodes, increases removal of the target species far beyondconventional adsorption that occurs on untreated electrodes.

A preferred average pore mouth diameter is in the range of 0.8 nm to 50nm, and a more preferred average pore mouth diameter range is 2 nm to 20nm. The applied potential causes redox reactions of the target species(e.g., plating, oxidation, reduction, peroxidation, etc.), and drivesfaradaic reactions on the carbon electrodes that will change the localpH regions at the anode (acidic) and cathode (basic). The combination ofreactions of the target species and the change in pH is controlled bythe applied potential. Applied E is typically at constant voltage andwill reach a nearly constant current at steady state. Generallyspeaking, the applied voltage dictates which faradic reactions willoccur within an FPC. An FPC will remove target species from a throughstream without using treated (i.e., shifted E_(PZC)) electrodes, buttarget species removal may be greater in certain water chemistries whenusing treated electrodes. If treated electrodes are used, the workingvoltage window (the potential difference between anode E_(PZC) andcathode E_(PZC)) is typically in the range if 0.3 V to 1.23 V.

The FPC invention combines adsorption (physical and capacitive) oftarget species (e.g., lead, iron, manganese, cadmium, chromium,chlorine, chloramine, etc.) and immobilization (aka coagulation) of theadsorbed target species by optimizing electrode porosity, applied E, andPourbaix operating region. The optimization of (i) physical adsorption;(ii) capacitive adsorption; (iii) electrochemical pH modulation & targetspecies immobilization; (iv) electrochemical peroxide (H₂O₂) generation;(v) electrodeposition (e.g., electroplating, electrophoreticdeposition); (vi) electrochemical oxidation or reduction; (vii)precipitation; (viii) pore mouth diameter profile; (ix) electrodetreatment, (x) electrode spacing, and (xi) flow-by vs. flow-through vs.carbon block cell design, depends upon target species, input streamwater chemistry, and through stream water chemistry.

Reduction only occurs at the cathode of an FPC. Electrochemicalreduction is usually described as an applied potential to the cell. Thevoltage distribution between anode and cathode occurs spontaneouslybased on the amount of applied voltage, the material properties of theelectrodes, and the chemistry of the aqueous solution.

One embodiment of the invention is a capacitive coagulation system andmethod that uses one or more capacitive coagulation cells that removemetal ions or particulate metal for which a Pourbaix diagram exists,e.g. As, Se, Pb, Ni, Zn, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr,Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg,Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, from aninput stream by one or more of the following methods, each of which is aCCC Parameter: (i) physical adsorption; (ii) capacitive adsorption;(iii) electrochemical pH modulation & metal immobilization; (iv)electrochemical peroxide (H₂O₂) generation & metal oxidation; (v)electrodeposition (e.g., electroplating, electrophoretic deposition);(vi) electrochemical oxidation or reduction; (vii) precipitation; (viii)pore mouth diameter profile; (ix) electrode treatment, (x) electrodespacing, and (xi) flow-by vs. flow-through vs. carbon block cell design.A CCC can remove lead from water to produce water with leadconcentrations below the EPA action level of 15 ppb for potable orirrigation water.

Compared to prior art devices, Applicant's CCC has higher specificityfor lead and other metals, removes both dissolved and particulate leadand other metals, has a device lifetime that can be measured in yearsrather than days or weeks, and uses low cost materials. Applicant's CCCachieves its longevity and efficiency by combining electrochemistry andcarbon materials to provide a system that is not saturated, fouled, orinhibited by other constituents in the water such as iron, volatileorganic compounds (VOCs), particulates, and natural organic matter(NOM). Applicant's device lifetime is multi-fold longer than the priorart technologies of carbon filtration, ion-exchange filtration, zeoliteadsorbents, and reverse osmosis (RO).

Combining in a CCC an optimized PMD, applied E, chemical manipulations,and electrochemical manipulations facilitates immobilization(coagulation) of lead onto the carbon electrodes. The adsorbed lead ispermanently removed from solution (FIG. 13). This methodology is easilyadaptable and applicable to the treatment of iron, manganese, cadmium,chromium, and other metals and metal derivatives. “Tuning” a CCCprimarily means selecting (i) a voltage applied between CCC anodes andcathodes based on (ii) analyzing and selecting an operating region inthe target species' Pourbaix diagram, and (iii) selecting a pore mouthdiameter profile of the CCC carbon electrodes that maximizes removal ofa target species. The effluent from an CCC can be used without furtherprocessing or can be routed to one or more EDCs, CCCs, or prior artwater purification cells for further removal of other target species.Tuning can optionally be further optimized through electrode treatment.

Metal speciation and chemistries can be exploited to selectively removelead (and other target metals) from water with high efficacy andselectivity, regardless of water chemistry. Through this operation,Applicant's CCC (i) can electrochemically, chemically, and physicallyremove lead and other target species from drinking water sources,eliminating the need for multiple separation techniques that arecurrently necessary and driven by varying input stream conditions andpH, and (ii) solves the technical problem of providing a more efficient,less expensive, scalable device for purifying drinking water and processwater, especially a device that removes soluble and insoluble lead tobelow 15 ppb. Adjustment of pH of an input stream may be necessary toimprove agglutination of a target species, especially for removal ofmetals.

In an EDC embodiment of the FPC technology, the EDC Parameters are“tuned” to remove other non-metal target species, e.g., chlorine,chloramines, and other halides and halide derivatives, from the EDCinfluent. “Tuning” an EDC primarily means selecting (i) a voltageapplied between EDC anodes and cathodes based on (ii) analyzing andselecting an operating region in the target species' Pourbaix diagram,and (iii) selecting a pore mouth diameter profile of the EDC carbonelectrodes that maximizes removal of a target species. The effluent froman EDC can be used without further processing or can be routed to one ormore EDCs, CCCs, or prior art water purification cells for furtherremoval of other target species. Tuning can optionally be furtheroptimized through electrode treatment. Device features and benefits arelisted below and in Table 2 and Table 3 in the Drawings.

TABLE 2 Detailed benefits of PTW EDC for chlorine removal ParameterPrior Art PTW EDC Capacity (gallons) 1000 100,000 Free ClRemoval >99% >99% Residence Time (seconds) 80 10-15 Operating Cost($/1000 gallons) $20-$50 $0.1 Carbon Mass (g) 200+ 30 Footprint (sq ft)0.133 0.130

TABLE 3 Detailed benefits of PTW EDC for chloramine removal ParameterPrior Art PTW EDC Capacity (gallons) 100 >3000 Chloramine Removal 75-90%up to 99% Residence Time (seconds) 80 10-15 Operating Cost ($/1000gallons) $200-$500 $30 Carbon Mass (g) 200+ 30 Footprint (sq ft) 0.1330.130

An EDC or CCC optionally uses treated anodes and cathodes made of carbonin which the one or both electrodes' E_(PZC) has been shifted comparedto a pristine electrode E_(PZC). Shifting the E_(PZC) of an electrodecan change the kinetics of reactions occurring (either positively ornegatively). Whether to shift only anodes, or only cathodes, or bothtypes of electrode, and how much E_(PZC) shift to use, depends uponinput water chemistry and the target species.

Carbon electrodes are superior to metal electrodes in avoiding orreducing electrolysis, or water splitting, when potentials as high as 3V are applied to an electrode. An applied potential of more than 1.23 V(“overpotential”) can cause electrolysis of water, which producesdangerous hydrogen gas. Metal electrodes can cause hydrogen gasproduction at <2 V; in contrast, carbon electrodes can sustain higherapplied voltages while avoiding substantive water electrolysis.

The inventive steps of an EDC are: (i) decreased power consumptionrequired for reduction of chlorine and chloramines (responsible fortaste and odor) through specific carbon electrodes and applied voltage,(ii) can be used on-demand or as continuous treatment, (iii) veryscalable, simple design that provides significantly lower cost POU/POEdevices as well as lower cost municipal, commercial, and industriallarge-scale systems, (iv) similar performance to traditional carbonblocks (such as activated carbon/activated charcoal) but withsignificantly less carbon needed, (v) similar removal performance offree chlorine with a much shorter residence time, (vi) the use of lesscarbon, (vii) longer electrode life, especially for the removal ofchlorine and chloramine, (viii) finer control over specific removalamounts and output water quality, (ix) better control over balancingrate of target species removal vs. electrode life, and (x) FPCcost/benefit can be adjusted by choice of carbon for FPC electrodes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

During capacitive charging processes, a constant current or voltage isused to charge electrode surfaces for the purposes of energy storage,desalination, or other useful capacitive techniques. Charging andsubsequent discharging of electrodes is often carried out for thousandsof cycles over a range of voltages and currents, depending on theintended application. Carbon electrodes made of activated carbon areoften employed for these capacitive-based charging and dischargingprocesses due to (i) their high specific surface area and resulting highcapacitance, and (ii) opportunities to add functional groups to effectsurface modifications that improve, inter alia, metal and other targetspecies removal, energy storage and deionization (e.g., desalination ofseawater or brackish water). Activated carbon is a form of carbonprocessed to have numerous small, low-volume pores that increase thesurface area available for adsorption or chemical reactions. An FPC canbe used to purify wastewater, cooling water, laundry wastewater, waterto be purified for human consumption, water to be purified foragriculture, water to be purified for horticulture, water to be purifiedfor use in food, water to be softened, sea water to be purified forhuman consumption, water to be purified for laboratory use, brackishwater to be purified for human consumption or agriculture use, and waterto be purified for medical use.

The distribution of pore sizes in a carbon electrode is a critical FPCParameter that has been overlooked in the prior art of waterpurification.

Electrode properties are shown in Table 4; the electrode suppliers arerecited in the first column of Table 4. The pore size, or pore mouthdiameter (“PMD”), is extremely important in terms of maintaining chargepassed and is directly related to the lifetime of the EDC electrodes.PMD is customarily used as representative of the diameter of theassociated pore channel within a carbon electrode. FIG. 9 demonstratesthe effect of PMD on stability of charge passed. A pore channel (andeven the pore mouth) may “collapse” (more accurately, the pore becomesoccluded) after repeated cycles of application of a voltage or potentialfollowed by reverse voltage or potential (or short circuiting or opencircuiting of anode(s) and cathode(s)). The pore mouth becomes “roofed”and/or the pore channel becomes “closed”, decreasing the surface area ofthe carbon (esp., the pore channel diameter and length) so that the poreno longer functions effectively. A “roofed” pore mouth blocks access tothe interior of the pore. Pore mouth roofing and pore channel collapsecause a decrease in electrode performance and eventual failure of priorart cells.

TABLE 4 Carbon electrode properties Conductivity PMD Surface Area Carbon(S/cm) (nm) (m²/g) Calgon 0.2 1.2-3 1000-2000 Kynol 1.2 2.2 2000 FuelCell Earth 900 N/A <2

In an FPC, a target species, if ionized, bearing an electrical charge,or bearing a partial charge due to the asymmetric distribution ofelectrons in chemical bonds, can be attracted to the carbon electrodedue to the applied potential, which produces a driving force to move thetarget species close to (or in contact with) the carbon electrode.Non-ions and non-charged species of a target species can collide with anelectrode surface. Once in contact with the electrode surface, numerouspathways to immobilization of the target species can occur. Local andlarge pH swings can be controlled to electrochemically produce analkaline environment, which will produce, e.g., insoluble metal oxides,that precipitate near or on the electrodes and are entrapped inelectrode pores. Faradic reactions, such as oxygen reduction reactionsat the cathode, can produce hydrogen peroxide which can diffuse awayfrom the electrode and oxidize target metal molecules that are withinclose proximity: hydrogen peroxide performs indiscriminate oxidation.When target species closer to the electrode are in a localized higherconcentration, the statistical chance for hydrogen peroxide to oxidizethe target species is greater. Other faradic reactions, such as directelectron transfer (reduction or oxidation) between the target speciesand electrode can also occur. Once the target species has been attractedto the electrode surface, the carbon electrode can (1) transfer anelectron(s) from the electrode to the target species and reduce it sothat it is deposited onto the electrode or (2) transfer an electron(s)from the target species to the carbon electrode and oxidize the targetspecies into either an insoluble oxide or hydroxide, or into a morereactive species that can be immobilized through additional electrontransfer reactions or pH adjustments. Precipitated species andelectrically attracted species are entrapped in electrode pores.

The size and volume of actual pores in activated carbon depend upon theshape, tortuosity (which is usually associated with changes in porediameter), and channel length of a given pore. Based on micrographs ofactivated charcoal, and depending on the activation and/or synthesisprocedures, some pores in activated carbon can be tubular channels,polygonal channels, spheroid chambers, surface slits, etc. Channels andchambers can be “dead end” or “through” (i.e., a channel or chamber withtwo surface appearances, aka “pore mouths”, with channel continuitybetween the two pore mouths). Pores in activated carbon are generalizedas being tubular channels that have an average pore channel diameter(hereinafter “pore channel diameter”) and an average pore mouthdiameter. Measuring actual pore channel diameter of billions of poresthat rarely have a constant pore channel diameter in a mass of activatedcarbon is a herculean task, and not reported here. As a generalization,the pore channel diameter is assumed to be identical to the pore mouthdiameter.

The diameter of a pore mouth, i.e., the opening of a pore toelectrolyte, has a major, and in small pore mouth diameters,predominant, impact on the utilization of that pore for adsorption andon multi-cycle performance in capacitive coagulation. A larger poremouth diameter (and therefore, pore mouth surface area) will providesignificant contact area between the pore channel and the electrolyte. Asmall pore mouth diameter will have more limited contact area (i.e.,“pore mouth surface area”). Pore mouth diameters are defined by IUPAC asmicroporous, mesoporous, and macroporous with pore mouth diameters of <2nm, 2-50 nm, and >50 nm, respectively. The lifetime of an adsorptionmedium has a direct correlation to the pore mouth diameter present onthe surface of the material. The concept and ramifications of “poremouth roofing”, aka pore mouth closure, after repeated cycles ofadsorption and desorption using an activated carbon electrode, isexplained below. A pore mouth “roofs” or “closes”, and a pore channel“collapses”, after repeated polarity reversal cycles of an FPC so thatthe surface area of the pore no longer functions effectively inentrapment and adsorption of target species.

Applicant's device incorporating capacitive coagulation technologyremoved soluble (dissolved) and insoluble (particulate) lead speciesfrom tap water to well below the EPA action level in samples spiked withconcentrations up to ˜300 ppb lead. Efficient lead removal was evendemonstrated with concentrations of lead as low 5 ppb in input streams,well below the action level. The prototype device achieved ≥90%, andfrequently >99%, specificity for lead removal over other constituentscommonly found in tap water, such as calcium (Ca²⁺). Applicant'scapacitive coagulation invention was able to achieve this performance inhard, alkaline water where lead species tend to form complexationspecies that are difficult to remove by commercial off-the-shelfproducts. A CCC is also unexpectedly capable of removing both soluble(dissolved) and insoluble (particulate) lead, arsenic, nickel, andcopper species.

Applicant's capacitive coagulation invention provides in one embodimentfor lead removal a POU/POE water purification device capable of meetingNSF/ANSI 53 and 61 certifications at a minimum flow rate of 1 gallon perminute (gpm) regardless of input water source conditions: hardness, pH,alkalinity, and types of disinfection. Additionally, the device is (i)highly specific for target metals, e.g., arsenic, lead, nickel, copper,cadmium, lead, manganese, mercury, and radioactive metals, (ii) morereliable, (iii) more efficient, and (iv) lasts longer thanstate-of-the-art solutions. Applicant's capacitive coagulation cellsprovide a more efficient, less expensive, and very scalable waterpurification device that removes soluble and insoluble lead to below 15ppb and is suitable for residential as well as scale-up tohigher-throughput systems. A detailed Example below focuses on leadremoval using capacitive coagulation cells, but adjustment of CCCparameters permit “tuning” of a CCC to remove any other metal or metalderivative for which a Pourbaix diagram exists, such as arsenic,cadmium, manganese, and mercury, as well as Se, Ni, Zn, Al, Sc, Ti, V,Cr, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta,W, Re, Os, Ir, Pt, Au, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, and Lu.

In a head-to-head comparison shown in FIG. 3, Applicant's CCCoutperformed commercially available POU/POE water purification devices,such as the Brita® Longlast™ and Brita® PUR filters and the Calgon GACfilter material. The Brita® Longlast™ pitcher filter had drasticallydifferent performance when tested on two different days based on thechange in water chemistry being supplied by the municipal water systemin Lexington, Ky. This differing performance emphasizes the need for amore reliable device that performs well in varying water chemistriesthat occur from day-to-day. Applicant's invention outperformed theBrita® Longlast™ device in both instances.

Soluble lead ions adsorb onto the carbon electrodes by physical and/orchemical adsorption, a process that is well documented (J. Chem.Technol. Biotechnol. 2002, 77, 458-464, Shekinah, P.; Kadirvelu, K.;Kanmani, P.; Senthilkumar, P.; Subburam, V. and Carbon. 2004, 42,3057-3069, Swiatkowski, A.; Pakula, M.; Biniak, S.; Walczyk, M.), andundergo additional electro-adsorption onto the cathode under an appliedpotential. Modulation of the pH can also be exploited to control leadspeciation in tap water. At an operating voltage of 1.2 V (as shown inFIG. 4), the potential distribution across the device yields +0.9 V atthe anode and −0.3 V at the cathode, and the pH fluctuates between theelectrodes, producing a near neutral pH in the bulk. However, while thebulk pH remains relatively constant, there are significant pH swings(aka “plugs”) from as acidic as pH 2 and as alkaline as pH 10, whichimpart significant changes in acid/base chemistry on an electrodesurface. Relating the voltage and pH at each electrode to a Pourbaixdiagram, operating conditions can be selected to obtain the desired leadspeciation in a given water chemistry (FIG. 4, where DIC is dissolvedinorganic carbon). A similar approach to manipulating pH was utilized toremove boric acid using capacitive deionization (CDI). ElectrochimicaActa. 2011, 56, 248-54, Avraham, E.; Noked, M.; Soffer, A.; Aurbach, D.For most residential and commercial uses, input stream pressure is lessthan 60 psi, and the porosity of the electrodes typically avoids morethan a 20 psi drop at an FPC outlet compared to inlet pressure.

Multiple mechanisms of action occur simultaneously for lead removalduring operation in a CCC: physical and electrochemical adsorption, pHmodulation yielding acid/base chemistry, and electrochemical/chemicaloxidation generating lead oxides and other insoluble species. The effectof applied potential and H₂O₂ generation on lead removal from tap waterwas verified by experimental data. As shown in Table 5, there is somephysical adsorption of lead with the carbon electrodes at open circuit.At short-circuit there is a slight improvement in lead removal, but themost dramatic result occurs at an applied voltage of 1.2 V, where thelead concentration drops to nearly 0 ppb. “Feed” is the input stream,and “treated” is the output stream, in the CCCs used in the experiments.

TABLE 5 Lead removal at different applied potentials Pb²⁺ ConcentrationApplied Potential Sample (ppb) None Feed 57.28 (open circuit) Treated16.14 0 V Feed 55.26 (short-circuit) Treated 10.14 1.2 V Feed 38.04Treated 2.89

FIG. 4, in the Pourbaix diagram of lead (Pb) in a carbonate aqueoussolution, shows the Pourbaix operating regions for lead species removalin a CCC at the intersection of E applied to anode and cathode. In aflow-through cell, FIG. 2 shows that the pH region at the start of thecathode is acidic (pH 2-3) while at the start of the anode, it is basic(pH 9-10). In a flow-through cell design (FIG. 2), these pH regions area result of the reactions that take place at the electrode surfaces andyield fluctuations in pH from 2-10. In FIG. 4, Pb²⁺ is in solutionequilibrium in most of the white area (approximately pH 7) between thedarker PbO₂(s) and Pb(s) areas; however, in the solution nearest theanode and cathode, Pb²⁺ becomes (i) reactive or (ii) immobilized asother Pb species. FIG. 5 shows the reaction mechanisms by which Pb isremoved from solution. In a flow-through cell, the alkaline (pH 9 to pH10) region near the anode (at applied E of 0.9 V, emanating from the pHgenerated from the cathode), Pb²⁺ is immobilized (adsorbed on the anode)as PbCO₃-2Pb(OH)₂, 2Pb(OH)₂, and PbO₂. In the alkaline region near theanode, Pb²⁺ also forms ionic compounds and lead hydroxide (as shown inthe middle box of FIG. 5) that are then oxidized into PbO₂, Pb₃O₄, andPb(OH)₂, which reaction products are then immobilized (adsorbed). Alsoin a flow-through cell, hydrogen peroxide, generated at the cathode fromdissolved oxygen reduction and combined with the acidic pH emanatingfrom the anode (pH 2 to pH 3) with an applied E of −0.4 V is a potentoxidizer. Hydrogen peroxide diffuses into the through stream, includingthe region near the anode where it oxidizes lead species in theintermediate reactions described above. The immobilized lead species arethereby removed from solution. Additional lead species are susceptibleto immobilization through reactions with hydrogen peroxide that isgenerated via oxygen reduction at the cathode (“peroxidation cell”).Water Research. 2017, 120, 229-237, Tang, W.; He, D.; Zhang, C.;Kovalsky, P.; Waite, T. D. In a hybrid system, FPCs can be using inseries with peroxidation cells to provide increased lead removal.

In an EDC, a cascading series ofchemical-electrochemical-chemical-electrochemical reactions areoccurring to decompose free chlorine and chloramine. The pH andoperating voltage are correlated through the Pourbaix diagram for atarget species. Examples are given below for hypochlorite, hypobromite,and monochloramine and shown in FIG. 6, FIG. 7 and FIG. 8, respectively.Based on the pH and potential distributions at each electrode, thetarget speciation can be controlled by selecting the pH and voltage toapply. This calibration process determines and controls what species aredecomposed at what voltage and in a given influent water chemistry. InFIGS. 6-8, the y-axis is voltage applied between the anode and cathodevs. a standard hydrogen electrode (SHE), and the x-axis is pH.

With reference to FIG. 6, at anode potential of <1.5 V vs. NHE and atotal cell potential of <2.5 V applied across anode and cathode,electrochemically generated hydrogen peroxide reacts with “freechlorine” in solutions with pH >7. Direct electrochemical reduction ofhypochlorous acid (HOCl) and hypochlorite (OCl⁻) from the carbon cathodeconverts them into free chloride ions and water. The chloride ion isthen capacitively adsorbed (immobilized). While there is no upper limitto the pH (e.g., H₂O₂ can be used to dechlorinate effluent fromcaustic/chlorine odor scrubbers), as a practical matter, pH 8.5 ispreferred in order to provide an instantaneous reaction.

With reference to FIG. 7, a Pourbaix diagram for hypochlorite, at ananode potential <1.2 V vs. NHE, a cathode potential of >−1.0 V vs. NHE,and a total cell potential of <2.2 V applied across anode and cathode,electrochemically generated hydrogen peroxide reacts with “free bromine”in solutions with pH >7. Direct electrochemical reduction of hypobromousacid (HOBr) and hypobromite (OBr⁻) from the carbon cathode converts theminto free chloride ions and water. The bromine ion is then capacitivelyadsorbed (immobilized).

With reference to FIG. 8, a Pourbaix diagram for mono chloramine, at ananode potential <1.4 V vs. NHE, a cathode potential of >−1.0 V vs. NHE,and a total cell potential of <2.4 V applied across anode and cathode,direct electrochemical changes in chloramine under acidic conditionsproduces the ammonium salt. Electrochemically generated (at an EDCcathode) hydrogen peroxide reacts directly with chloramine to produce amixture of products: chloride ions, nitrite ions, protons (acid), andwater. Chloramine reacts with electrochemically generated hydrogenperoxide to produce ammonia which will react further in 2 ways: 1)reaction with electrochemically generated hydrogen peroxide to yieldnitrogen and hydrogen gas and water, or 2) reaction with acid to yieldammonium salts. Chloramine will also react directly withelectrochemically generated acid in a cascade process to yieldtrichloramine which is converted into hypochlorous acid in water.

EDCs typically operate with total cell potential of <3.0 V appliedacross anode and cathode; depending upon target species and input waterchemistry, total cell potential of <3.0 V applied across anode andcathode in an EDC is usually between 1.0 V to 3.0 V.

As shown in FIG. 9, the active surface area of SC, KN, and CG carbonelectrodes decreases from exposure to cycles of an applied voltage. CX'sspecific charge passed is stable over repeated cycles, but is lower thanthe other carbons tested. In contrast, Applicant's HE electrode,formulated with PMD, performs better than the other electrodes afterabout 220 cycles, and maintains superior performance. In the SC, KN, CG,and CX electrodes, oxide groups form on the surface causing pore roofingand pore collapse, resulting in increased resistance (bulk oxidation).Alternatively, oxide groups can form a resistive oxide layer (surfaceoxidation). Both scenarios require that the applied voltage increase,according to Ohm's law, to maintain the same amount of current tocompensate for this increase in resistance: V=IR, where V is voltage(V), I is current (A), and R is resistance (a).

FIG. 10 shows that at a given applied voltage there will be a potentialdistribution between the anode and cathode in a CCC; the voltage willsplit between the electrodes, which may not be equal. For example, if1.6 V is applied to an FPC, the cathode may be at −0.9 V vs. SCE and theanode at +0.7 V vs. SCE (FIG. 10). This in turn affects the FPCoperating parameters and frequency of polarity-switching performed ineach cycle of operation in an EDC. The active surface area, carbonmaterial, and applied voltage, among other things, affect the potentialdistribution. The E_(PZC) of an electrode affects the distribution ofapplied E during the initial use of an electrode, and the potentialdistribution changes slightly. Balancing of faradic reaction rates atthe anode and cathode ultimately stabilize potential distribution

Accelerated oxidation studies, shown in FIG. 11, show the effect of pore“collapse and roofing” observed with microporous carbon. This emphasizesthat mesoporous carbons can handle a large applied voltage whilemaintaining charge efficiency and avoiding the effect of pore collapseand roofing. Careful selection of PMD used in an FPC device greatlyincreases device reliability and lifetime, and thereby reduces watertreatment costs.

A bench-scale CCC system is shown in FIG. 12. The capacitive coagulationsystem provides >50% lead removal selectivity vs. non-metal ions. InCCCs tuned (using CCC Parameters) to remove lead (“lead-removal CCC”),lead removal can approach 100%. In one embodiment of a lead-removal CCC,various oxygen-based surface groups are added to the electrode and leadremoval below 15 ppb is achieved in all cases for ˜50 ppb lead tap waterinput stream, at a CCC operating voltage of 1.2 V. Using carboxylfunctionalized electrodes (aka treated electrodes), as described in U.S.application Ser. No. 62/702,286 incorporated herein, a lead-removal CCCreduced the concentration of lead in the output stream to only 0.05 ppb,equating to 99.9% removal efficiency.

The removal selectivity of dissolved lead was consistently ≥99% comparedto Ca²⁺ for the treatment of a consecutive 5 gallons of tap water withconcentrations as high as ˜10 ppm lead (Table 6), as confirmed by ICP-MSand calculated as percent removal of species. Scanning electronmicroscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysesof the electrodes after filtration confirmed lead immobilization areshown in FIG. 13.

TABLE 6 Lead removal selectivity Volume % Removal Pb²⁺ Treated ~300 ppbFeed ~10 ppm Feed 1 gallon 99.69 99.99 2 gallons 99.83 99.99 3 gallons99.95 99.98 4 gallons 99.93 99.98 5 gallons 99.48 99.97 Removal ≥99% inall cases Selectivity

To further study the effect of applied potential on lead removal, tapwater spiked with lead was filtered with a packed column filled withactivated carbon at no applied potential (passive filtration/physicaladsorption) and compared to CCCs operated at 1.2 V (activefiltration/capacitive coagulation). The same amount of carbon and flowrate was used for both experiments. Breakthrough curves for thesestudies are shown in FIG. 14. The packed column initially adsorbed lead,denoted by the abrupt drop in concentration, but after only ˜0.3 L ofwater had passed through the carbon it began to saturate. In contrast,CCCs were able to filter 5 gallons (˜19 L) of water up to an astonishing10,000 ppb and maintain performance, consistently removing lead below aconcentration of 2 ppb. This extrapolates to an estimated devicecapacity of ≥1 g of lead removed per gram of carbon electrode. Theprototype device shown in FIG. 9 would yield an overall capacity of ≥500g of lead, equating to a theoretical volume capacity of ˜8.8 milliongallons assuming an input stream concentration of 150 ppb lead; otherfactors impact CCC performance in POU configurations and yield apredicted CCC volume capacity of 100,000 gallons. In contrast, currentPOU filters only have a volume capacity of approximately 1,500 gallons.

Additionally, the dissolved oxygen (DO) dropped to ˜10% of saturation,equating to <1 ppm DO, and 1.25 ppm of H₂O₂ was measured afterfiltration at an applied potential of 1.2 V (FIG. 15). Theseobservations reveal that lead removal is influenced by a combination ofpotential and H₂O₂ generation. The Pourbaix diagram in FIG. 4 emphasizeshow sensitive lead speciation is to modest changes in water chemistry,such as fluctuations in pH and voltage. The combination of thesemechanisms yield the benefits observed with capacitive coagulation usedin CCCs.

To test the limitations of Applicant's CCC device, tap water with leadconcentrations as low as 5 ppb and as high as 10,000 ppb were processedthrough CCCs. Lead was successfully removed in all cases at an appliedvoltage of 1.2 V (Table 7). Even at highly dilute conditions wherepassive filtration consisting of equilibrium-based adsorption struggle,the capacitive coagulation's active filtration process excels with aselectivity of ≥99% (Table 6).

Key CCC device performance improvements over prior art devices: 99.9%lead removal ≥99% selectivity maintained down to ~5 ppb lead Active leadfiltration system developed (capacitive coagulation) Permanent leadremoval

TABLE 7 Lead removal at 1.2 V Sample Pb²⁺ Concentration (ppb) Feed 5.63Treated 1.45 Feed 54.32 Treated 0.05 Feed 295.72 Treated 0.15 Feed10,000 Treated 0.28

Higher throughput CCC systems are fabricated by adding more capacitivecoagulation cells and/or using larger electrodes in each cell. Suchlarger systems provide lead removal efficacy from 150 ppb to ≤10 ppb ata flow rate of 1 gpm or higher.

The preferred applied E for removal of Al, Ag, Au, Br, Cl, Co, Cu, Fe,Hg, Ir, Mn, Pb, Pd, Pt, Ni, Zn, and chloramine using an FPC are shown inTable 1.

CCC systems remove lead to below EPA action levels even if the inputstream has various combinations of lead content, water hardness,alkalinity, disinfectants, and pH. Water chemistry will impact leadspeciation (e.g., day to day variations in municipal water chemistry,the effect of which are shown in FIG. 4 above). Currently there does notexist one device that can treat lead in all of its forms; prior artdevices typically use physical entrapment at higher pH and zeolite mediaat lower pH. In contrast, CCCs can remove lead in all forms (species)commonly found in drinking water sources.

Different operating parameters were explored depending on the watertype. Corrosion of internal materials is a common concern withelectrochemical-based systems, however little evidence of corrosion hasbeen observed in FPC systems; internal components are designed, and thematerial is chosen, to be extremely robust, stable, and inert togalvanic and chemical corrosion. In one embodiment of the invention, iflead is found to leach after on/off operation or from the addition ofchloramines, the FPC system can be designed to switch to open circuit ora small potential when not in use, and an inexpensive carbon blockpre-filter is added to remove chloramines. An optional post-filter isadded if small pieces of the carbon cloth are found to flake off overtime.

Operational adjustments for specific water chemistries. Analysis oftypical input stream feeding a given FPC device permits adjustments tooptimize operating parameters for specific water chemistries(adjustments are to optimize physical and electrochemical adsorption oflead, pH modulations, and oxidation to lead oxides and other insolublespecies). Typical operating parameters are adjusted as follows:

Operating voltage. To obtain the potential distribution, athree-electrode set-up is used with a cathode, anode, and a standardcalomel electrode (SCE) as the reference. The potential at eachelectrode is recorded at open circuit, short-circuit, and up to avoltage of 1.4 V with 0.2 V increments. The pH and operating voltage arecorrelated through the Pourbaix diagram. Based on the pH and potentialdistributions at each electrode, the lead speciation can be controlledby selecting what voltage to apply. This calibration process determinesand controls what lead species precipitate at what voltage and in agiven input stream water chemistry.

Oxygen reduction and 11202 generation. Oxygen reduction at the cathodegenerates H₂O₂ that can react with lead species to facilitate theformation of lead oxides. There is a significant reduction in DO at anapplied voltage of 1.2 V and measured 1.25 ppm H₂O₂ in the filteredwater. The operating voltage is controlled to amplify this reaction formaximal lead removal. Experiments conducted at open circuit,short-circuit, and up to a voltage of 1.4 V with 0.2 V increments, andthe pH, DO, and H₂O₂ concentrations at the outlet typically remove leadto below EPA action levels.

Carbon conductivity. FPC devices typically use a microporous carbon witha moderate conductivity (carbon B in Table 8). A comparative study ofcarbons with different properties, Table 8, was conducted to elucidatetheir effect on lead removal via capacitive coagulation.

TABLE 8 Carbon properties Conductivity Pore Size Surface Area Carbon(S/cm) (nm) (m²/g) A 0.2 1.2-3 1000-2000 B 1.2 2.2 2000 C 900 N/A <2

The CCC lead removal technology relies on (i) physical adsorption; (ii)capacitive adsorption; (iii) electrochemical pH modulation and metalimmobilization; (iv) electrochemical peroxide (H₂O₂) generation & metaloxidation; (v) electrodeposition (e.g., electroplating, electrophoreticdeposition); (vi) electrochemical oxidation; (vii) precipitation; (viii)pore mouth diameter profile, (ix) electrode treatment, (x) electrodespacing, and (xi) flow-by vs. flow-through vs. carbon block cell design.A combination of these factors, or a cascade of these factors, causesspeciation and immobilization of target species that become trapped inthe pore network of the carbon electrodes, which results in a purifiedeffluent. It is imperative that the carbon electrodes are conductive.The more conductive the carbon material, the more uniform the currentdistribution was across the electrodes, which typically results inincreased H₂O₂ generation and a more efficient lead removal process. Thepore size and surface area are related to the adsorption capacity andtortuosity of the material. Pore size and surface area also affect H₂O₂generation in an FPC device.

POU/POE device design. A POU/POE FPC product design parameters include:(1) Residence time and size of device was identified to achieve a flowrate of 1.5 gpm; and (2) Effective lead removal, defined by a reductionin dissolved lead levels from 150 ppb to <10 ppb and removalselectivity >90% over non-metal divalent ions, at 1.5 gpm for at least150 gallons of water treated.

Residence time of the water: The residence time is a measure of theaverage time a volume of water remains in the device (volume/flow rate).In other words, it is the time required to filter a given amount ofwater. The internal volume of the device and flow rate dictates theresidence time. In the bench-scale CCC device, at a flow rate of 20ml/min, a residence time of 5 min typically gives the desired removal.The residence time for the flow rate at which the performance reaches apeak is selected as the design specification and the device is sizedappropriately.

Pressure drop: The pressure drop across a FPC device is increasinglyimportant as the flow rate increases. A pressure drop of <20 psi isconsidered acceptable and is below a normal inlet water pressure forresidential and municipal buildings of ˜45 psi.

Ultimate capacity of a FPC device. For NSF/ANSI certification, the leadconcentration must be reduced from 150 to 10 ppb, and POU systems on themarket are rated to treat up to 120 gallons of water. This translatesinto ˜1 gallon of water treated per gram of carbon for a pitcher systemand ˜1.6 gallons of water treated per gram of carbon for anunder-the-sink system. One embodiment of the CCC device can treat 2gallons of water at 1.5 gpm to bring lead levels from 150 ppb to ≤10ppb. Ultimate capacity of the system is obtained from a lead removalcurve. Pressure drop issues typically arise after >1 g of lead removalper gram of FPC carbon electrode. CCC embodiments for POU/POE use caninclude a lead sensor and/or pressure drop sensor to alert a user toreplace the device.

FPC replacement threshold ranges for various embodiments. In general, aCCC is replaced when the target metal concentration in the output streamexceeds the relevant threshold level, e.g., 15 ppb for leadconcentration and 1.3 ppm for copper (see the Lead and Copper Rule, aregulation published by the EPA in 1991(https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations).The threshold level (aka sorption capacity) could be specified by agovernment agency, or user selected. Municipal and industrial wastewaterdischarge limits are different from drinking water limits; the metalconcentration thresholds are typically higher. There are effluentguidelines for different industries (https://www.epa.gov/eg).

FPC Regeneration. When a FPC output stream metal concentration equals orexceeds the threshold level, rather than replacing the FPC, some typesof FPCs can be regenerated (e.g., in a CCC, the adsorbed metal ions andparticles desorbed (removed) from the CCC electrodes). One method of CCCregeneration is by flushing acid through the cell to dissolve coagulatedmetals and regenerate the electrodes. During this “acid regeneration”step, the output stream is diverted to a receptacle in which the highlyconcentrated waste stream is collected for other processing. After anacid regeneration step, the CCC is flushed with water until the outputstream reaches pH 7 (or other target pH) before normal CCC operation(i.e., removal of metal ions and particles from the through stream) isresumed. Another method of CCC regeneration is by electrolysis orelectrochemical regeneration in an acidic solution; electrolysis (akaelectrochemical) regeneration converts metal oxides to soluble metalions, which are then flushed out of the CCC with water and collected ina waste receptacle. Electrolysis is an electrochemical reaction thatrequires the application of an external voltage to drive a reaction thatis non-spontaneous. Any insoluble metal species that have formed on theelectrodes can be dissolved into solution using a small voltage,typically up to 5 V, applied across the CCC. CCC regeneration can alsobe a sequence of acid regeneration followed by electrolysis, or viceversa.

Multiple FPCs, in series, each of which FPCs targets the same or adifferent species. Multiple FPCs connected in series (outlet to inlet)tuned to remove the same target species act to successively reduce theconcentration of the target species in a single pass of an input streamthrough the FPCs connected in series (accomplishing the same level oftarget species removal as operating a single cell in batch mode multipletimes). Adjustment of FPC Parameters, e.g., pH of the through stream andvoltage applied to the cell electrodes of a given cell, of multiplecells connected in series to different FPC Parameters and EDCParameters, as the case may be, enable each cell in a series to remove adifferent target species from the through stream in a single pass.Pourbaix diagrams, which show the speciation of a target species at agiven voltage and pH, best illustrate the “cell series” concept.Pourbaix diagrams for lead (FIG. 16) and copper (FIG. 17) are used toexplain the immobilization of different metals in a CCC series. Thehorizontal dashed lines represent the applied voltage; the appliedvoltage can move along the vertical axis. The vertical dashed linesrepresent the pH; the pH can move along the horizontal axis. The regionwhere these lines intersect represents the species of the metal thatwill exist at these conditions. The operating conditions depicted inFIG. 16 and FIG. 17a would immobilize (adsorb on a CCC electrode) Pb andCu as PbO_(2(s)) (FIG. 16) and Cu(OH)_(2(s)) (FIG. 17), effectivelyremoving each metal from the feed stream. The operating conditionsdepicted in FIG. 17b would electrodeposit or electroplate Cu on theelectrode as Cu_((s)). Pourbaix diagrams for nickel, iron, manganese,aluminum, and zinc have also been included (FIG. 18 to FIG. 22). Asimilar approach to manipulating the applied voltage and pH can be takento remove these metals. The operating conditions selected to forminsoluble species may differ for each target species, and there could beseveral possibilities for a given target species depending on thespeciation depicted in the Pourbaix diagram.

Applied voltage and electrochemical pH modulation are selected to removetarget species of Ni, Fe, Mn, Al, and Zn from CCC influent using thePourbaix diagrams shown in FIGS. 18-22, respectively, as explainedbelow. Those of skill in the art can select an applied voltage andelectrochemical pH modulation to remove a given species of a targetelement or complex. Copper is removed by the CCC via electrodeposition,hydroxide precipitation, and/or oxidation to copper oxides.

FPC control system. FPC Parameters for a given FPC are monitored andcontrolled using a computer system that monitors and/or controls varioussensors, interfaces, valves, and peripheral equipment, and is commonlyknown as a process control computer (aka process controller), a computergenerally associated with continuous or semi-continuous productionoperations involving materials such as chemicals and petroleum, whetherin liquid, solid, or gas phases. The process control computer enablesFPC Parameters to be applied to one or more FPCs in a system and changesin through-stream routing, e.g, changes that convert a series systemarchitecture to a series-parallel system architecture.

Extension of FPC design to other target species for which Pourbaixdiagrams exist. In addition to Pb, Ni, Zn, Al, Cu, Fe, Mn, Cl, Br, andchloramine, the FPC Parameters, and the system and methods disclosedabove, can be applied to remove a metal and halide species identified inthe Pourbaix diagrams for As, Se, Sc, Ti, V, Cr, Co, Y, Zr, Nb, Mo, Tc,Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Ce, Pr, Nd,Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and other halides.

Examples

Performance tests of EDCs were conducted to verify removal of totalchlorine, free chlorine, chloramine, and peroxide (H₂O₂) using carbonelectrodes and voltages of <3.0 V. Measurements were made usinganalytical test kits. Experiments were conducted with a flow-by celldesign and 14 pairs of electrodes in an alternating series ofanode-cathode-anode-cathode (variable number of repeats ofanode-cathode) anode-cathode (FIG. 23). In the flow-by design shown inFIG. 23, the input stream proceeds through an annular space near thewall of the cell container, then flows centripetally over the electrodesurfaces to the axial channel, and is then discharged through the axialchannel to the FPC outlet. A positive voltage is applied to the anodesand a negative voltage is applied to the cathodes. The polarity of thevoltage applied to a given electrode is periodically switched(converting each anode into a cathode, and each cathode into an anode)to ensure that all electrodes degrade at the same rate and to extend thelifetime of the EDC device. An example is shown in FIG. 24. Thepolarity-switching interval for a given EDC can be arbitrarily set(e.g., every hour) or can be set based on one or more EDC parameters,e.g., current threshold, voltage threshold, rate of current decrease atconstant voltage, percentage of current decrease at constant voltage,rate of voltage decrease at constant current, percentage of voltagedecrease at constant current, total volume treated, and concentration oftarget species in EDC effluent. Preferred polarity-switching points are(i) a percentage decrease in current at a constant applied voltage, (ii)a percentage increase in voltage at a constant applied current, (iii)total volume treated, and (iii) concentration of target species ineffluent. Depending on a target species, percentage decreases orincreases may be detected before a rise in concentration of the targetspecies in the effluent is detected, or vice versa (see Figures belowplotting V vs. concentration of target species in effluent). Three typesof carbon were examined. Electrode properties are shown in Table 4.

Capacitive coagulation experiments were conducted to test Cu removalusing 16 pairs of carbon electrodes (˜13 g of carbon), in which thecathodes were pristine SC and the anodes were nitric acid oxidized SC.The FPC was operated at short-circuit (0 V). A 1 L feed solution of ˜100ppm Cu [Cu(NO₃)₂] in direct injection (“DI”) H₂O was treated at a flowrate of 20 ml/min. Samples were analyzed by inductively coupled plasma(ICP) with optical emission spectrometer (OES) and the results in Table9 show that approximately ⅓ of the Cu was removed in a single pass.

TABLE 9 ICP-OES results for Cu²⁺ removal Sample Cu²⁺ Concentration (ppm)Untreated 96 Treated 66

Capacitive coagulation experiments were conducted to test Cu removalusing 12 pairs of carbon electrodes (˜10 g of carbon), in which thecathodes and anodes were both pristine SC. The FPC was operated at anapplied potential of 1.2 V on the cathode. A 18.5 L feed solution of ˜50ppm Cu [Cu(NO₃)₂] and ˜50 ppm Ca (CaCl₂)) in DI H₂O was treated at aflow rate of 20 ml/min. During operation Cu plated out of solution ontothe cathode, shown as a grayish deposit in FIG. 25 a.

Flow-by capacitive coagulation experiments were conducted to test Curemoval using 14 pairs of carbon electrodes (˜30 g of carbon), in whichthe cathodes were nitric acid oxidized KN and the anodes were pristinecarbon. The FPC was operated at applied potentials of 0.8, 1.0, and 1.2V. A 1.5 L feed solution of ˜2 ppm Cu [Cu(NO₃)₂] in tap H₂O was treatedat a flow rate of 100 mL/min. Samples were taken before and afterfiltration with the cell and the Cu²⁺ concentration measured withICP-OES. ˜78% Cu removal was achieved at all conditions tested (Table10).

TABLE 10 ICP-OES results for Cu²⁺ removal from tap water Sample Cu²⁺Concentration (ppm) Removal (%) Untreated 2.30 n/a Treated at 0.8 V 0.5277.5 Treated at 1.0 V 0.52 77.6 Treated at 1.2 V 0.52 77.6

Flow-by capacitive coagulation experiments were conducted to test Curemoval at low pH using 14 pairs of carbon electrodes (˜30 g of carbon),in which the cathodes were nitric acid oxidized KN and the anodes werepristine carbon. The FPC was operated at 1.2 V. A 1.5 L feed solution of˜10 ppm Cu [Cu(NO₃)₂] in tap H₂O was treated at a flow rate of 100mL/min. The pH was adjusted to 2.8 using concentrated H₂SO₄. Sampleswere taken before and after filtration with the cell and the Cu²⁺concentration measured with ICP-OES. Cu was very effectively removed(Table 11), with a removal of 99.8%.

TABLE 11 ICP-OES results for Cu²⁺ removal from tap water at pH 2.8Sample Cu²⁺ Concentration (ppm) Removal (%) Untreated 10.29 n/a Treated0.02 99.8

Flow-by capacitive coagulation experiments were conducted to test Niremoval using 14 pairs of carbon electrodes (˜30 g of carbon), in whichthe cathodes were nitric acid oxidized KN and the anodes were pristinecarbon. The FPC was operated at applied potentials of 0.8, 1.0, and 1.2V. A 1.5 L feed solution of ˜50 ppm Ni [Ni(Cl)₂] in tap H₂O was treatedat a flow rate of 100 mL/min. Samples were taken before and afterfiltration with the cell and the Ni²⁺ concentration measured withICP-OES. The highest removal of ˜63% was achieved at 1.2 V (Table 12).

TABLE 12 ICP-OES results for Ni²⁺ removal from tap water Sample Ni²⁺Concentration (ppm) Removal (%) Untreated 49.21 n/a Treated at 0.8 V36.96 24.9 Treated at 1.0 V 24.56 50.1 Treated at 1.2 V 18.36 62.7

Capacitive coagulation experiments were conducted to test Fe removalusing 16 pairs of carbon electrodes (˜14 g of carbon), in which thecathodes were pristine SC and the anodes were nitric acid oxidized SC.The cell was operated at short-circuit (0 V). A 18.5 L feed solution of100 ppm Fe [Fe(Cl)₃] or 25 ppm FeCl₃ in DI H₂O was treated at a flowrate of 20 ml/min. The concentration of Fe steadily decreased withtreatment, ICP-OES results are shown in Table 13. For the higherconcentration experiment (100 ppm Fe), Fe-oxides formed at the cathodeas rust-colored precipitates on the separators, shown as a grayishdeposit (FIG. 26).

TABLE 13 ICP-OES results for Fe²⁺ removal Fe²⁺ Concentration Sample(ppm) Untreated 5.73 Treated 0.10

Flow-by capacitive coagulation experiments were conducted to test Feremoval using 14 pairs of carbon electrodes (˜30 g of carbon), in whichthe cathodes were nitric acid oxidized KN and the anodes were pristinecarbon. The FPC was operated at applied potentials of 0.8, 1.0, and 1.2V. A 1.5 L feed solution of ˜15 ppm Fe [Fe(Cl)₃] in tap H₂O was treatedat a flow rate of 100 mL/min. Samples were taken before and afterfiltration with the cell and the Fe³⁺ concentration measured withICP-OES. ˜99.9% Fe removal was achieved at all conditions tested (Table14).

TABLE 14 ICP-OES results for Fe²⁺ removal from tap water Sample Fe²⁺Concentration (ppm) Removal (%) Untreated 15.37 n/a Treated at 0.8 V0.015 99.9 Treated at 1.0 V 0.012 99.9 Treated at 1.2 V 0.013 99.9

Flow-by capacitive coagulation experiments were conducted to test Mnremoval using 14 pairs of carbon electrodes (˜30 g of carbon), in whichthe cathodes were nitric acid oxidized KN and the anodes were pristinecarbon. The FPC was operated at applied potentials of 0.8, 1.0, and 1.2V. A 1.5 L feed solution of ˜20 ppm Mn [Mn(SO₄)] in tap H₂O was treatedat a flow rate of 100 mL/min. Samples were taken before and afterfiltration with the cell and the Mn²⁺ concentration measured withICP-OES. ˜99.8% Mn removal was achieved at 1.2 V (Table 15).

TABLE 15 ICP-OES results for Mn²⁺ removal from tap water Sample Mn²⁺Concentration (ppm) Removal (%) Mn Feed 18.93 n/a Treated at 0.8 V 8.4355.5 Treated at 1.0 V 0.53 97.2 Treated at 1.2 V 0.041 99.8

Flow-by capacitive coagulation experiments were conducted to test Alremoval using 14 pairs of carbon electrodes (˜30 g of carbon), in whichthe cathodes were nitric acid oxidized KN and the anodes were pristinecarbon. The FPC was operated at applied potentials of 0.4, 0.8, and 1.2V. A 1.5 L feed solution of ˜30 ppm Al from a wastewater sample wastreated at a flow rate of 100 mL/min. Samples were taken before andafter filtration with the cell and the Al³⁺ concentration measured withICP-OES. ˜99.9% Al removal was achieved at 0.4 V (Table 16).

TABLE 16 ICP-OES results for Al³⁺ removal from tap water Sample Al³⁺Concentration (ppm) Removal (%) Feed 31.58 n/a Treated at 0.4 V 0.0599.9 Treated at 0.8 V 5.84 81.5 Treated at 1.2 V 12.05 61.8

Flow-by capacitive coagulation experiments were conducted to test Znremoval using 14 pairs of carbon electrodes (˜30 g of carbon), in whichthe cathodes were nitric acid oxidized KN and the anodes were pristinecarbon. The FPC was operated at applied potentials of 0.4, 0.8, and 1.2V. A 1.5 L feed solution of ˜35 ppm Zn [Zn(C12)] in tap H₂O was treatedat a flow rate of 100 mL/min. Samples were taken before and afterfiltration with the cell and the Zn²⁺ concentration measured withICP-OES. ˜40.8% Zn removal was achieved at 1.2 V (Table 17).

TABLE 17 ICP-OES results for Zn²⁺ removal from tap water Sample Zn²⁺Concentration (ppm) Removal (%) Feed 35.39 n/a Treated at 0.8 V 23.7532.9 Treated at 1.0 V 22.95 35.1 Treated at 1.2 V 20.94 40.8

To study the physical adsorption of Pb on pristine and oxidized Kynol,packed columns were filled with ˜5 g of carbon and 1 L of ˜100 ppm Pb[Pb(NO₃)₂] in DI H₂O was filtered at a flow rate of 20 mL/min. Theresults in Table 18 provide evidence that Pb is physically adsorbing tothe carbon. Additionally, there was considerable white precipitate onthe pristine Kynol electrodes after filtration (FIG. 27) that wereconfirmed by energy dispersive X-ray spectroscopy (EDX) to be lead oxide(FIG. 28).

TABLE 18 ICP results for treated water after flowing through packedcolumns Pb²⁺ Concentration (ppm) Sample Pristine Nitric acid oxidizedFeed 73.87 94.94 1^(st) pass 6.12 32.33 4 h 17.11 36.45 *Conductivityreading was 0 μS/cm

Flow-through capacitive coagulation experiments with a 1 L feed solutionof ˜50 ppb Pb [Pb(NO₃)₂] in tap H₂O, 12 pairs of pristine carbonelectrodes HO g), and a flow rate of 20 mL/min, showed Pb removal towell below the federal action level of 15 ppb in a single pass (Table 19and Table 20). The cell was operated at short-circuit (0 V) and anapplied potential of 0.8 and 1.2 V. Pb was spiked in several times totest removal. The experiments in Table 20 were performed with pristineanodes and nitric acid oxidized cathodes at 1.2 V. Samples were takenbefore and after filtration through the cell and the Pb²⁺ concentrationmeasured with a handheld sensor from ANDalyze and/or inductively coupledplasma mass spectroscopy (ICP-MS). “\” in the Tables means “notmeasured”.

TABLE 19 Results for feed and treated water with Kynol anodes andcathodes Pb²⁺ Concentration ICP-MS Sample (ppb)* (ppb) Feed 45, 58 44.961.2 V <12  1.21 Spike 1 50 \ 0.8 V <12 \ Spike 2 ~50 \ 0.8 V <2  \ Spike3 ~50 \ 1.2 V <2  \ Spike 4 32 \ 1.2 V Single pass 3 \ *Measurementstaken with ANDalyze sensor

TABLE 20 Results for feed and treated water with pristine Kynol anodesand nitric acid oxidized Kynol cathodes Pb²⁺ Concentration ICP-MS Sample(ppb)* (ppb) Feed (50 ppb Pb) 21, 44, 51 51.72 sample 1 <2  0.2 sample 2<2  \ Spike 1 >100 \ sample 1 12, 17 \ sample 2 <2  \ sample 3 <2  \Spike 2 ~50  \ sample 1 <2  \ sample 2 <2  \ sample 3 <2  \ sample 4 3 \Spike 4 23 19.9 Single pass <2  2.18 *Measurements taken with ANDalyzesensor

Flow-by capacitive coagulation experiments with 1.5 L feed solutions of˜5 to ˜275 ppb Pb [Pb(NO₃)₂] in tap H₂O, 14 pairs of carbon electrodes(˜30 g), pristine anodes and nitric acid oxidized cathodes, and a flowrate of 100 mL/min, also showed Pb removal to well below the federalaction level of 15 ppb in a single pass (Table 21) The cell was operatedat an applied potential of 1.2 V. Samples were taken before and afterfiltration with the cell and the Pb²⁺ concentration measured with ahandheld sensor from ANDalyze and/or ICP-MS. From the results it wasmade clear that Pb was being permanently removed from solution.

TABLE 21 Results for feed and treated water with pristine Kynol anodesand nitric acid oxidized Kynol cathodes Pb²⁺ Concentration ICP-MS Sample(ppb)* (ppb) Feed ~50  \ sample 1 <2  \ sample 2 <2  \ sample 3 <2  \Spike 1 >100 \ sample 1 <2  \ Spike 2 5 54.32 sample 1 <2  0.05 Spike 374 \ sample 1 <2  \ Spike 4 39 \ sample 1 <2  \ Spike 5 17 5.63 Singlepass - 1.2 V <2  1.45 Spike 6 - 15 ppb Pb 11 \ sample 1 2 \ Spike 7 *150 ppb Pb 300 273.22 sample 1 12 12.17 *Measurements taken withANDalyze sensor

Flow-through capacitive coagulation experiments with a 1 L feed solutionof ˜50 ppb Pb [Pb(NO₃)₂] in tap H₂O, 12 pairs of carbon electrodes (˜10g), and a flow rate of 20 mL/min were carried out at open-circuitvoltage (OCV), short-circuit (0 V), and applied potentials of 0.4 to 1.4V with 0.2 V increments. Various oxygen-containing surface groups weretested, as well as carbons with differing properties. Samples were takenafter a single pass through the cell and the Pb²⁺ concentration measuredwith a handheld sensor from ANDalyze and/or ICP-MS.

The experimental results in Table 22 are for pristine anodes and citricacid oxidized cathodes. Pb was removed at OCV and short-circuit, but wasmore effectively removed under applied potential. The best result wasobtained at 1.2 V, where 92% of the Pb was removed.

TABLE 22 Pb removal results for pristine Kynol anodes and citric acidoxidized Kynol cathodes Pb²⁺ Concentration ICP-MS Sample (ppb)* (ppb)Spike 1 - 50 ppb 90 40.09 Single pass - OCV 22 13.44 Spike 2 - 50 ppb 7257.28 Single pass - OCV 12 16.14 Spike 3 - 50 ppb 104 68.40 Singlepass - short-circuit 5 12.02 Spike 4 - 50 ppb \ 55. Single pass -short-circuit \ 10.14 Spike 5 - 50 ppb 86 67.98 Single pass - 0.4 V 1413.36 Spike 6 - 50 ppb 72, 90 61.41 Single pass - 0.6 V 2, 5 7.26 Spike7 - 50 ppb 32 26.94 Single pass - 0.8 V 13 8.99 Spike 8 - 50 ppb 5250.70 Single pass - 1.0 V 31 10.04 Spike 9 - 50 ppb <2 38.04 Singlepass - 1.2 V \ 2.89 Spike 10 - 50 ppb \ 29.91 Single pass - 1.4 V \ 7.26Spike 11 (150 ppb) \ 129.41 Single pass - 1.2 V \ 5.32 *Measurementstaken with ANDalyze sensor

The experimental results in Table 23 are for pristine anodes and nitricacid oxidized cathodes. The measured concentrations of Pb are below thespiked value of ˜50 ppb. The pH was close to 9 and there was likelyinsoluble Pb species not being accounted for in the measurement. Anorange precipitate was also observed on the last pristine piece ofcarbon (anode), visible on the perimeter of the filter paper.

TABLE 23 Pb removal results for pristine Kynol anodes and nitric acidoxidized Kynol cathodes Pb²⁺ Concentration ICP-MS Sample (ppb)* (ppb)Spike 1 - 50 ppb >100, 112 58.33 Single pass - OCV >100, 48  27.51 Spike2 - 50 ppb \ 13.69, 12.15 Single pass - OCV \ 26.60, 25.19 Spike 3 - 50ppb 6 5.70 Single pass - short-circuit <2 5.40 Spike 4 - 50 ppb <2, 304.06 Single pass - short-circuit 10 5.00 Spike 5 - 50 ppb <2, 15 2.52Single pass - 0.4 V <2 4.39 Spike 6 - 50 ppb \ 3.09 Single pass - 0.6 V\ 1.95 Spike 7 - 50 ppb <2 2.42 Single pass - 0.8 V 8 2.24 Spike 8 - 50ppb \ 24.38 Single pass - 1.0 V \ 6.67 Spike 9 - 50 ppb \ 17.87 Singlepass - 1.2 V \ 9.51 Spike 10 - 50 ppb \ 3.83 Single pass - 1.4 V \ 22.31Spike 11 (150 ppb) \ 10.52 Single pass - 1.2 V \ 2.92 *Measurementstaken with ANDalyze sensor

The experimental results in Table 24 are for pristine anodes and ovenoxidized cathodes at 340° C. for 72 h. Pb removal was observed atshort-circuit and 1.2 V. The dissolved oxygen (DO) was also monitoredthroughout the experiment and decreased with applied voltage, suggestingthat oxygen is being reduced to H₂O₂ (Table 25).

TABLE 24 Pb removal results for pristine Kynol anodes and oven oxidizedKynol cathodes Pb²⁺ Concentration ICP-MS Sample (ppb)* (ppb) Spike 1 -50 ppb 19 24.9 Single pass - OCV 3 3.7 Spike 2 - 50 ppb \ 9.4 Singlepass - short-circuit \ 0.9 Spike 7 - 50 ppb >100 34.0 Single pass - 1.2V <2  0.8 *Measurements taken with ANDalyze sensor

TABLE 25 Conductivity (κ), pH and DO values for samples listed in Table2 κ DO Sample (μS/cm) pH (%) Spike 1 - OCV 450 4.90 46.3 Spike 2 -short-circuit 473 6.15 59.8 Spike 3 - 1.2 V 217 6.04 17.3

Three carbons were tested: Kynol, Zorflex, and Fuel Cell Earth. Theirproperties are listed in Table 26. Results using Zorflex are shown inTable 27 and Table 28. The DO decreased and lead removal improved withapplied voltage.

TABLE 26 Carbon properties Conductivity Pore Size Surface Area Carbon(S/cm) (nm) (m²/g) Zorflex 0.2 1.2-3 1000-2000 Kynol 1.2 2.2 2000 FuelCell Earth 900 N/A <2

TABLE 27 Pb removal results for pristine Zorflex anodes and nitric acidoxidized Zorflex cathodes Pb²⁺ Concentration ICP-MS Sample (ppb)* (ppb)Spike 1 >100 36.1 Single pass - OCV 23 8.1 Spike 2 ~50  59.7 Singlepass - short-circuit \ 9.6 Spike 7 ~50  67.5 Single pass - 1.2 V 17 5.0*Measurements taken with ANDalyze sensor

TABLE 28 Conductivity (κ), pH, and DO values for samples listed in Table26 κ DO Sample (μS/cm) pH (%) Spike 1 - OCV 644 6.16 64.2 Spike 2 -short-circuit 639 6.33 65.5 Spike 3 - 0.4 V 611 6.55 68.3 Spike 4 - 0.6V 591 6.60 54.4 Spike 5 - 0.8 V 626 6.84 58.4 Spike 6 - 1.2 V 440 6.21 6.6

Results using Kynol are shown in Table 18-Table 24, as well as below inTable 29, Table 32 and Table 36. For the results shown in Table 29 onlyOCV, short-circuit, and an applied potential of 1.2 V were tested. Leadremoval to very low levels even at a starting concentration of ˜10 ppbwas achieved, and the DO concentration dropped to below 6% at 1.2 V.SEM/EDX confirmed Pb deposits on the electrodes (FIG. 13).

Fuel Cell Earth (www.fuelcellstore.com) is a graphitic cloth and ishighly conductive. Results are shown in Table 30 and Table 31. There wasno measurable current in either case, owing to its very low surfacearea. When the cell was taken apart after the first experiment (Table30) there was orange precipitate on all filter paper, regardless oflocation in the cell. The experiment was repeated with pristine carbonfor both the anode and cathode, and samples were taken after 3 h ofcycling as opposed to a single pass (Table 31). In this case there wasno lead removal at open circuit, some at short-circuit, and much more atan applied potential of 1.2 V. The DO remained unchanged regardless ofapplied potential, and H₂O₂ was measured to be 0 ppm at 1.2 V. Pbremoval is likely occurring due to pH swings at the electrode surfaceand not by reacting with H₂O₂.

TABLE 29 Pb removal results for pristine Kynol anodes and nitric acidoxidized cathodes κ DO Pb²⁺ Concentration Sample (μS/cm) pH (%) (ppb)Spike 1 508 6.30 43.9 29.1 Single pass - OCV 423 6.91 56.4 5.3 Spike 2 \\ \ 34.6 Single pass - short-circuit 421 7.05 60.6 7.7 Spike 274 6.4620.0 36.8 36.8 Single pass - 1.2 V 270 6.54 15.6 5.4 (3*) Spike 4 3056.35 16.2 14.6 Single pass - 1.2 V 301 6.40 14.7 5.2 Spike 5 299 6.3312.2 8.9 Single pass - 1.2 V 297 6.29 12.2 0.6 (<2*) Spike 6 - 1.2 V 3266.10 10.2 \ *Measurements taken with ANDalyze sensor

TABLE 30 Pb removal results for pristine Fuel Cell Earth anodes andnitric acid oxidized Fuel Cell Earth cathodes Pb²⁺ Concentration ICP-MSSample (ppb)* (ppb) Spike 1 48 31.1 Single pass - OCV 3 3.5 Spike 4 \85.7 Single pass-short-circuit 17 15.2 Spike 9 65 42.0 Single pass - 1.2V <2 2.4 Spike 14 ~50 \ Single pass - 80 ml/min 1.2 V <2 1.7*Measurements taken with ANDalyze sensor

TABLE 31 Pb removal results for pristine Fuel Cell Earth anodes andcathodes κ DO Pb²⁺ Concentration Sample (μS/cm) pH (%) (ppb) Spike 1 \ \\ 125 Single pass - OCV 671 7.73 61.4 125 Spike 2 671 7.73 61.4 125Single pass - short-circuit 562 7.87 66.2 85 Spike 3 562 7.87 66.2 85Single pass - 1.2 V \ \ \ 28 3 h - 1.2 V 596 8.11 68.0 3 Spike 4 6718.28 71.4 ~150 3 h - OCV 670 8.29 70.4 146 Spike 5 670 8.29 70.4 146 3h - 1.2 V 627 8.18 71.1 5 *Measurements taken with ANDalyze sensor

The same series of experiments as described above was conducted with Pbspiked into synthetic tap water (Table 32 and Table 33 This water didnot contain any carbonates and had a similar concentration of otherionic species in our tap water. Pb removal was observed at OCV andshort-circuit, with slightly more removal at 1.2 V. The DO concentrationwas low throughout the experiment.

TABLE 32 Pb removal results for pristine Kynol anodes and nitric acidoxidized cathodes in synthetic tap water Pb²⁺ Concentration ICP-MSSample (ppb)* (ppb) Spike 1 63 58.7 Single pass - OCV <2  6.1 Spike2 >100 86.5 Single pass - 1.2 V 5 6.4 Spike 3 \ 12.7 Single pass - 1.2 V\ 3.6 Spike 7 31 \ Single pass - 0.6 V 11 \ *Measurements taken withANDalyze sensor

TABLE 33 Conductivity (κ), pH and DO values for samples listed in Table31 κ DO Sample (μS/cm) pH (%) Spike 1-OCV 468 5.16 7.30 Spike 2-1.2 V350 6.02 5.94 Spike 3-1.2 V 329 5.89 5.22 Spike 7-0.6 V 452 6.12 6.01

Breakthrough curves were obtained for packed columns of pristine ornitric acid oxidized carbon (˜5 g) and 1 L of ˜150 ppb Pb [Pb(NO₃)₂ tapH₂O was filtered at a flow rate of 20 mL/min (Table 34 and Table 35). Inthis case, Pb removal is occurring via physical adsorption (passivefiltration) as opposed to capacitive adsorption and coagulation (activefiltration) with our device. The initial Pb concentration decreasesdramatically, but both carbons saturate quickly at ˜0.3 L of watertreated and become ineffective. Pristine carbon appears to be moreeffective for physical adsorption of lead as compared to oxidized carbonat the conditions tested. To determine when a flow-through embodiment ofa FPC device becomes saturated, 5 gallons of water were treated at 1.2 Vin a single pass with 12 pairs of electrodes (˜10 g) at 20 mL/min.Sustained performance for 5 gallons of water treated was obtained (Table36). The concentration of lead remained low after filtration, whereasthe concentration of calcium (Ca²⁺) was approximately constant,demonstrating a selectivity >99% for lead. This experiment was repeatedwith a flow-by device where 5 gallons of water were treated at 1.2 V ina single pass with 14 pairs of electrodes (˜30 g) at 100 mL/min (Table37). Pb removal was maintained for the total volume passed, even from anextremely high starting Pb concentration.

TABLE 34 Results for treated water after flowing through packed columnof pristine Kynol (reduced carbon) Sample Pb²⁺ Concentration (ppb)* Feed120 1 min 5 3 min 13 5 min 41 15 min 66 30 min 46 45 min 56*Measurements taken with ANDalyze sensor

TABLE 35 Results for treated water after flowing through packed columnof nitric acid oxidized Kynol (oxidized carbon) Sample Pb²⁺Concentration (ppb)* Feed 178 1 min <2 15 min 128 30 min 116 45 min 106*Measurements taken with ANDalyze sensor

TABLE 36 Results for 5 gallons of treated water with pristine Kynolanodes and nitric acid oxidized cathodes from ~300 ppb Pb feed solutionPb²⁺ Concentration Ca²⁺ Concentration κ DO ANDalyze ICP-MS ICP-MS Sample(μS/cm) pH (%) (ppb) (ppb) (ppb) Feed 458 7.00 17.3 275 295.72 42.21 1gallon 470 7.10 17.2 <2 0.92 42.29 2 gallons 470 7.14 16 <2 0.50 44.72 3gallons 479 7.09 11.4 <2 0.15 44.83 4 gallons 488 7.25 10.4 <2 0.1947.05 5 gallons \ \ \ <2 1.53 47.27

TABLE 37 Results for 5 gallons of treated water with pristine Kynolanodes and nitric acid oxidized cathodes from ~10,000 ppb Pb feedsolution Sample Pb²⁺ Concentration (ppb)* ICP-MS (ppb) Feed ~10,0002149.42 1 gallon <2 0.28 2 gallons \ 0.29 3 gallons \ 0.38 4 gallons \0.49 5 gallons <2 0.58 *Measurements taken with ANDalyze sensor

A flow-by capacitive coagulation experiment with a 1.5 L feed solutionof ˜150 ppb Pb [Pb(NO₃)₂] in tap H₂O, 14 pairs of carbon electrodes (˜30g), and a flow rate of 300 mL/min was carried out at and appliedpotential 1.2 V (Table 38). Samples were taken before and after a singlepass through the cell and the Pb²⁺ concentration measured with ahandheld sensor from ANDalyze. The treated sample was at the limit ofdetection of the sensor.

TABLE 38 Lead removal at 300 mL/min Sample Pb²⁺ Concentration (ppb)Removal (%) Untreated ~150 n/a Treated 2 97.73

A flow-by capacitive coagulation experiment with a 1.5 L feed solutionof ˜150 ppb Pb [Pb(NO₃)₂] in tap H₂O at a pH of 2.83, adjusted withconcentrated H₂SO₄, 14 pairs of carbon electrodes (˜30 g), and a flowrate of 100 mL/min was carried out at and applied potential 1.2 V (Table39). Samples were taken before and after a single pass through the celland the Pb²⁺ concentration measured with a handheld sensor fromANDalyze. The treated sample was below the limit of detection of thesensor.

TABLE 39 Lead removal at pH 2.83 Sample Pb²⁺ Concentration (ppb) Removal(%) Untreated 88 n/a Treated <2 97.73

A flow-by capacitive coagulation experiment with a 1.5 L feed solutionof ˜150 ppb Pb in a Pb-acid battery manufacturer wastewater sample, 14pairs of carbon electrodes (˜30 g), and a flow rate of 100 mL/min wascarried out at and applied potential 1.2 V (Table 40). Samples weretaken before and after a single pass through the cell and the Pb²⁺concentration measured with a handheld sensor from ANDalyze. Theeffluent was well below the assigned Pb discharge limit of 0.6 ppm.

TABLE 40 Lead removal at pH 2.83 Sample Pb²⁺ Concentration (ppb) Removal(%) Untreated 88 n/a Treated <2 97.73

A rolled cell design was used for capacitive coagulation experimentswith a 1.5 L feed solution of ˜150 ppb Pb [Pb(NO₃)₂] in tap H₂O, ˜14 gof carbon electrodes, pristine anodes and nitric acid oxidized cathodes,and flow rates of 50, 100, and 200 mL/min, all showed Pb removal tobelow the federal action level of 15 ppb in a single pass (Table 41).The cell was operated at an applied potential of 1.2 V. Samples weretaken before and after filtration with the cell and the Pb²⁺concentration measured with a handheld sensor from ANDalyze.

TABLE 41 Lead removal results for a rolled cell design Sample Pb2⁺Concentration (ppb) Removal (%) Untreated 122 n/a Treated at 50 ml/min 893.4 Untreated ~150 n/a Treated at 100 ml/min 8 94.7 Untreated ~150 n/aTreated at 200 ml/min 13 91.3

A rolled cell design was used for capacitive coagulation experimentswith a 1.5 L feed solution of ˜50 ppb Pb [Pb(NO₃)₂] and 2.5 ppm Pb intap H₂O, as well as ˜10 ppm Cu in tap water. Pb removal was below thefederal action level of 15 ppb for the lower concentration and <1 ppmfor the higher concentration (Table 42). Cu removal was >99% (Table 43).A schematic of a rolled cell is shown in FIG. 29.

TABLE 42 Results for Pb removal from tap water with a rolled cellarchitecture. Feed 2 was adjusted to pH 5.08 with sulfuric acid. PbSample (ppm) Feed 1 0.028* Treated 1 <0.002* Feed 2 2.45** Treated 20.83** *Measurement taken with ANDalyze sensor **ICP-OES measurements

TABLE 43 ICP-OES results for Cu removal from tap water with a rolledcell architecture. The feed was adjusted to pH 2.4 with sulfuric acid.Cu Sample (ppm) Feed 9.67 Treated <0.01

A series cell architecture was used for capacitive coagulationexperiments with a solution of 2.5 ppm Pb [Pb(NO₃)₂] in tap H₂O and ˜30g of carbon electrodes at 1.2 V. A consecutive 5 gallons of water weretreated and concentrations were consistently below 48 ppb (Table 44).

TABLE 44 ICP-OES results for Pb removal from tap water with a seriescell architecture. The feed was adjusted to pH 5 with sulfuric acid. PbSample (ppm) Feed 2.53 2 Gallons Treated 0.015 3 Gallons Treated 0.026 4Gallons Treated 0.045 5 Gallons Treated 0.048

Carbon blocks were used for capacitive coagulation experiments with a1.5 L feed solution of ˜50 ppb Pb [Pb(NO₃)₂] in tap H₂O (Table 45). Pbremoval was below the federal action level of 15 ppb.

TABLE 45 ICP-OES results for Pb removal from tap water with a carbonblock architecture. Pb Sample (ppb) Feed 55.35 Treated 4.48

Industrial wastewater containing multiple metal species, Cu, Fe, and Mn,at concentrations in the ppm range was used for flow-by capacitivecoagulation experiments. Flow rates of 0.5, 1.0, and 1.5 L/min weretested at 1.2 V. Cu was reduced by >98%, Fe by >14%, and Mn by >87%(Table 46).

TABLE 46 ICP-OES results for metals removal from an industrialwastewater sample at increasing flow rates. The feed was adjusted to pH5 with sulfuric acid. Ca concentration remains unchanged, demonstratingthe exceptional selectivity of the cell for metals. Feed Treated (ppm)Parameter (ppm) 0.5 L/min 1.0 L/min 1.5 L/min Ca 60.53 63.12 61.71858.21 Cu 4.39 0.083 0.071 0.070 Fe 0.34 0.0008 0.0007 0.0007 Mn 0.430.18 0.15 0.11

Reverse osmosis (RO) concentrate, or brine, containing multiple metalspecies, Cu, Fe, and Mn, at concentrations in the ppb range was used forflow-by capacitive coagulation experiments. Flow rates of 0.1, 0.5, and1.0 L/min were tested at 1.2 V. Cu was reduced by >99%, Fe by >99%, andMn by >74% (Table 47).

TABLE 47 ICP-MS results for metals removal from reverse osmosis (RO)brine at increasing flow rates. Feed Treated (ppb) Parameter (ppb) 0.1L/min 0.5 L/min 1.0 L/min Cu 9.85 <0.034 <0.034 0.75 Fe 14.56 2.95 4.176.50 Mn 105.57 13.07 24.06 41.43

Total and free chlorine were measured before and after treatment with anEDC tuned for chlorine removal. Chloramine was estimated from thedifference between total and free chlorine. Free chlorine removalof >99% and chloramine removal of up to 99% was obtained. A voltage <3.0V was applied to the cell during operation. Flow rates of 100 to 500ml/min were tested. A total of ˜210 gallons of water was treated beforedegradation in performance was observed, strictly due to charge lossfrom pore collapse.

Oxidized Kynol (nitric acid treatment) was used as the anode andpristine Kynol as the cathode when V >0; electrodes are switched whenV<0. Total chlorine in the feed (influent) and product (effluent)streams is shown in FIG. 30; a clear reduction of total chlorine in theeffluent was observed. FIG. 31 and FIG. 32 show the concentration offree chlorine and chloramine in the feed and product streams,respectively. FIG. 33 shows the % removal of each disinfectant. Freechlorine removal of >99% and chloramine removal of ˜80% was obtained.Peroxide removal of up to 100% was also achieved after treatment withthe EDC.

Oxidized Kynol (nitric acid treatment) was used as the cathode and FuelCell Earth as the anode. Total chlorine in the feed and product streamsis shown in FIG. 34; a clear reduction of total chlorine in the effluentwas observed at an applied voltage of 2.0 V. FIG. 35 and FIG. 36 showthe concentration of free chlorine and chloramine in the feed andproduct streams, respectively. FIG. 37 the % removal of eachdisinfectant. Free chlorine removal of >99% and chloramine removal of˜40% was obtained. Peroxide removal of ˜60% was also achieved aftertreatment with the EDC.

Oxidized Calgon (nitric acid and electrochemical treatment) was used asthe anode and pristine Calgon as the cathode when V >0; electrodes areswitched when V<0. Total chlorine in the feed and product streams isshown in FIG. 38; a clear reduction of total chlorine in the effluentwas observed. FIG. 39 and FIG. 40 show the concentration of freechlorine and chloramine in the feed and product streams, respectively.FIG. 41 shows the % removal of each disinfectant. Free chlorine removalof up to 96% and chloramine removal of ˜57% was obtained. Peroxideremoval of ˜57% was also achieved after treatment with the EDC.

SUMMARY

In summary, the FPC invention comprises an electrochemical device forpurifying an aqueous solution, wherein at least one carbon-based anodeand at least one carbon-based cathode (each such anode and cathode beinga pristine electrode without E_(PZC) shift) alternate within a containerconfigured with at least one inlet that supplies an aqueous solution tothe container, at least one outlet that discharges purified output fromthe container, a separator is disposed between each electrode, and apower supply with associated wiring provides a DC constant voltage orconstant current to the carbon-based electrodes, wherein an aqueoussolution containing at least one target species to be removed from theaqueous solution is admitted through the inlet, passes by or through theelectrodes to a discharge channel that leads to the at least one outlet,wherein the DC voltage applied to the at least one anode and the DCvoltage applied to the at least one cathode are DC voltages shown in aPourbaix diagram of the at least one target species at which the atleast one target species is agglutinated on an electrode through amechanism selected from the group consisting of capacitive adsorption,faradic immobilization, and both capacitive adsorption and faradicimmobilization. The agglutination of the at least one target species iscaused oxidation of the target species in a pH region of <4 near the atleast one anode. Alternatively, the agglutination of the at least onetarget species is caused by oxidation of the target species in a pHregion of <4 near the at least one anode, wherein the oxidation arisesfrom production of oxidizers in a pH region of >10 near the at least onecathode. The power supply is controlled by a process controller ormanually. The material with which the electrodes are fabricated has highaqueous permeability and is selected from the group consisting ofactivated carbon cloth, a mixture of microporous and mesoporousactivated carbon, a mixture of mesoporous and macroporous activatedcarbon, and a mixture of microporous, mesoporous, and macroporousactivated carbon. The separator thickness is selected from the groupconsisting of a range of 1 nm to 100 microns, 2 nm to 50 microns, 2 nmto 30 microns, 1 to 100 microns, 1 to 50 microns, and 1 to 30 microns.The DC voltage used to achieve faradic immobilization is selected fromthe group consisting of less than 0.6 V, less than 1.2 V, and less than2.0 V. The electrodes can optionally be separated by an impermeableinsulator and wherein the through stream flows only through the porouselectrode before reaching a discharge channel, or by a permeableseparator wherein the through stream flows by the electrodes through theseparator to the discharge channel. An ion-exchange membrane canoptionally cover the at least one anode, the at least one cathode, orboth electrodes. The electrical potential of zero charge of at least onecarbon-based electrode can be shifted by a mechanism selected from thegroup consisting of reduction of a cathode, oxidation of a cathode,reduction of an anode, and oxidation of an anode. The spacing betweenelectrodes is selected from the group consisting of less than 1 mm, lessthan 200 microns, less than 50 microns, and less than 20 microns. Thecell design of an FPC can be rolled or stacked.

An anode in an FPC can have an average pore mouth diameter selected fromthe group consisting of an average pore mouth diameter of 2.0 to 10 nmachieved with a pore mouth diameter profile from 0% to 30% microporousactivated carbon and from 70% to 100% mesoporous activated carbon,wherein the microporous activated carbon comprises carbon with aconductivity value >10 S/cm, and an average pore mouth diameter 2.5 to10 nm achieved with a pore mouth diameter profile of 0% to 20%macroporous activated carbon and 80% to 100% mesoporous activated carbonwith a conductivity value >10 S/cm. A cathode in an FPC can have anaverage pore mouth diameter selected from the group consisting of anaverage pore mouth diameter of 2.0 to 10 nm achieved with a pore mouthdiameter profile from 0% to 30% microporous activated carbon and from70% to 100% mesoporous activated carbon, wherein the microporousactivated carbon comprises carbon with a conductivity value >10 S/cm,and an average pore mouth diameter 2.5 to 10 nm achieved with a poremouth diameter profile of 0% to 20% macroporous activated carbon and 80%to 100% mesoporous activated carbon with a conductivity value >10 S/cm.

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We claim:
 1. An electrochemical device for purifying an aqueoussolution, the electrochemical device comprising: at least onecarbon-based anode and at least one carbon-based cathode, the at leastone carbon-based cathode consisting essentially of a microporousactivated carbon cloth with a surface area of about 1800 or about 2000m²/g, and the at least one carbon-based anode consisting essentially ofa macroporous graphite cloth having a surface area of less than 2 meterssquared per gram (m²/g); a container comprising at least one inlet thatsupplies an aqueous solution to the container and at least one outletthat discharges purified output from the container, the aqueous solutioncomprising at least one target species to be removed, the at least onecarbon-based anode and the at least one carbon-based cathode arrangedwithin the container, and a separator arranged between each carbon-basedanode and adjacent carbon-based cathode; and a power supply withassociated wiring that provides a DC constant voltage to the at leastone carbon-based anode and the at least one carbon-based cathode, the DCconstant voltage being a voltage associated with a Pourbaix diagram ofthe at least one target species at which the at least one target speciesis agglutinated on the at least one carbon-based anode through faradicimmobilization and oxidation of the at least one target species in a pHregion of less than 4 near the at least one carbon-based anode.
 2. Thedevice of claim 1, wherein the oxidation arises from production ofoxidizers in a pH region of greater than 8 near the at least onecathode.
 3. The device of claim 1, wherein the power supply iscontrolled by a process controller or manually.
 4. The device of claim1, wherein the separator thickness is selected from the group consistingof a range of 1 nanometers (nm) to 100 micrometers (microns), 2 nm to 50microns, 2 nm to 30 microns, 1 to 100 microns, 1 to 50 microns, and 1 to30 microns.
 5. The device of claim 1, wherein the DC constant voltageused to achieve faradic immobilization is selected from the groupconsisting of less than 0.6 Volts (V), less than 1.2 V, and less than2.5 V.
 6. The device of claim 1, wherein the separator is a permeableseparator.
 7. The device of claim 1, wherein spacing between the atleast one carbon-based anode and the at least one carbon-based cathodeis selected from the group consisting of less than 1 millimeter (mm),less than 200 microns, less than 50 microns, and less than 20 microns.8. The device of claim 1, wherein the electrochemical device is a rolleddevice, a stacked device, or a carbon block device.
 9. The device ofclaim 1, wherein an average pore mouth diameter range of the at leastone carbon-based anode is greater than 50 nm, and target species andfaradic porosity cell (FPC) parameters are selected from the groupconsisting of: Manganese, with FPC parameters of anode voltage range of0 to 1.2 V vs. NHE, cathode voltage of less than −1.1 vs. NHE, andoperating voltage of 1.2 V; Iron, with FPC parameters of anode voltagerange of 0 to 1.2 V vs. NHE, cathode voltage of less than −0.5 V vs.NHE, and operating voltage range of 0.4 to 1.2 V; Cobalt, with FPCparameters of anode voltage range of greater than 0 V vs. NHE, andcathode voltage of less than −0.5 V vs. NHE; Nickel, with FPC parametersof anode voltage range of 0 to 1.0 V vs. NHE, cathode voltage of lessthan −0.4 V vs. NHE, and operating voltage of 1.2 V; Copper with FPCparameters of anode voltage of greater than 0 V vs. NHE, cathode voltageof less than 0 V vs. NHE, and operating voltage range of 0.8 to 1.2 V;Zinc, with FPC parameters of anode voltage of greater than 0 V vs. NHE,cathode voltage of less than −0.8 V vs. NHE, and operating voltage rangeof 0.8 to 1.2 V; Aluminum, with FPC parameters of anode voltage ofgreater than 0 V vs. NHE, cathode voltage of less than −1.3 V vs. NHE,and operating voltage of 0.4 V; Lead, with FPC parameters of anodevoltage of greater than 0.5 V vs. NHE, cathode voltage of less than −0.4V vs. NHE, and operating voltage of 1.2 V; Palladium, with FPCparameters of anode voltage of greater than 0 V vs. NHE, and cathodevoltage of less than 0 V vs. NHE; Silver, with FPC parameters of anodevoltage of greater than 0 V vs. NHE, and cathode of less than 0 V vs.NHE; Iridium, with FPC parameters of anode voltage of greater than 0.4 Vvs. NHE, and cathode voltage of less than 0 V vs. NHE; Platinum, withFPC parameters of anode voltage of greater than 0 V vs. NHE, and cathodevoltage of less than 0 V vs. NHE; Gold, with FPC parameters of anodevoltage of greater than 0.8 V vs. NHE, and cathode voltage of less than0 V vs. NHE; Mercury, with FPC parameters of anode voltage of greaterthan 0.3 V vs. NHE, and cathode voltage of less than 0 V vs. NHE;Chlorine, with FPC parameters of an anode potential of less than 1.5 Vvs. NHE and total cell potential of less than 2.5 V applied across anodeand cathode; Bromine, with FPC parameters of an anode potential lessthan 1.2V vs. NHE, a cathode potential of greater than −1.0 V vs. NHE,and a total cell potential of <2.2 V applied across anode and cathode;and Chloramine, with FPC parameters of an anode potential less than 1.4V vs. NHE, a cathode potential of greater than −1.0 V vs. NHE, and atotal cell potential of greater than 2.4 V applied across anode andcathode.